I figure that a lot of folk are familiar with the concept of min-maxing, although in many circles it has negative connotations. Some of it is justified, in that there are players who use their rules mastery to ruin the game or to engage in showboating. However, I often seen the disparagement come a little too frequently, or in the worst case scenarios willfully overlooking genuine design flaws because the person who discovered the glitch in question's a min-maxer (who must certainly be up to no good)!
I have an interesting story to share I saw several years ago on a D&D message board. Back in the early days of 3rd Edition D&D, there was a group of players which included a Fighter and a Druid who happened to score a prime spot of land for settlement. The adventurers wnt about making their home base in the area and doing some domain management. It was an exciting time for all at first, because who doesn't want to build a super-cool castle/secret base/etc? The Druid could be the nature dude tapping into primeval wellsprings while the Fighter gets to be a noble commander and leader of men as portrayed in plenty of fantasy media.
Things didn't work out that way. The party druid realized that his class abilities could contribute greatly to domain management. Wild shape into a harmless-looking bird and survey the area while being able to rain down lightning bolts on enemy encampments. Diplomacy was a class skill, meaning that the wildman was better able to negotiate with the other land barons at high society functions than the poor Fighter. The Fighter's bread and butter, his vast array of potential feat selection, was mostly limited to combat-related tricks he'd have to wait for another level to learn, whereas the druid could swap out his entire spell selection every day. And not just that, but the druid could wildshape into great beasts, potentially being able to strike enemies 15 feet away or even chaining up to 4 attacks at once on a full charge with Pounce (something martials could never replicate without excessive dumpster-diving for feats and prestige classes through scores of sourcebooks).
So what happened? The fighter's player accused the druid's player of showing him up and gaming the system, intentionally stepping on his toes and making his contributions to the party irrelevant. The druid was not utilizing 6+ combinations of splatbooks, nor juggling disparate modifiers to end up with insanely high bonuses. His player was merely using the resources given to him at his disposal, almost all of which were in the Core Rulebooks.
You see, 3rd Edition is one of the most unbalanced versions of D&D, even more so than a lot of OSR games. The way the game is structured is that a lot of restrictions on spell-casters in earlier Editions got mitigated or removed, and the bread and butter for martials (feats and class features) were much more restrictive than magic. Even more so, martials did not have great access to many skills, and a lot of the "role-playing skills" were based on mental scores or not class skills, meaning they got outshined by spellcaster and thief classes in that department. There's also been a demand among the playerbase and even a few game designers to limit noncasting martials to the domain of real-world physics (or more accurately what they imagined real-world physics to be like) crying "overpowered" whenever 3.X Fighters got nice things.
Lack of transparency led to the demand for min-maxing
The main problem in the previous example was fellow players thinking the worst of others at the table and jumping to conclusions, but this case of accidental upstaging is sadly very common in D20 games. 3rd Edition has not been playtested past 12th level, and the designers played the game like they did 2nd Edition AD&D, not utilizing a huge portion of their own new rules such as leaving spell slots open (which has been imported to Pathfinder) or playing non-healbot clerics. In fact, Ivory Tower Game Design intentionally left in trap options in the game which looked cool on paper but were not so much in actual play; this was an attempt to reward system mastery. Dragons were intentionally under-CRed to make them even more threatening to parties (leading to a lot of TPKs for poor GMs who were going by the game's rules and could not foresee it).
D20 is a great and versatile game system, but it's deeply broken. To prevent accidental nerfs and party members suddenly becoming useless at their own roles, min-maxing became a demand to help people avoid trap options. Combined with the sheer versatility and options through the amount of sourcebooks, as well as 3.0 being the first Edition to be birthed around the time of a widespread Internet, resulted in a subculture of sorts to grow on Wizards of the Coast's message boards. A community of min-maxers grew. Sometimes they tested out the limits of the system by creating utterly broken builds for theorycraft; sometimes they were more practical, writing handbooks which were the D&D equivalent of video game strategy guides; sometimes they helped out non-min-maxing player groups with advice on their current games and any potential mechanical pitfalls which may be lying in wait. Beyond just this one subforum, D20 min-maxing communities became known as "Character Optimization forums," or CharOps for short.
Sadly, the illusion of D20 balance has carried over to Pathfinder, which hailed itself as being an updated version which solved much of 3rd Edition's problems. Sadly, old problems were replaced with new ones, and the trends which led to imbalance in the first place (splatbooks full of new spells, unnecessary nerfs to martials, etc) were repeated over the course of the games' history.
Compare this to the OSR, which specializes in Original and Basic D&D and retroclones. They don't care about game balance, but there's no illusion of their games being such. It's generally accepted that certain classes are going to be more powerful than others at various levels of play, or characters in parties might contribute less due to poor die rolls and choices at character creation. However, this is more in the open, and the power disparity between casters and martials in these Editions isn't as wide (OSR fighters have the best saves in the game, unlike D20 D&D). As a result, there is not as much incentive for a CharOps culture to grow in the OSR because of this.
The disruptive min-maxer has a sad element of truth
D20 D&D is a rules-heavy game. In fact, it's one of the rules-heaviest RPGs on the marketplace. The sheer volume of text and sourceboks is unlike any other Edition, and while DM Fiat can be employed, small changes to the system ("we're removing alignment") result in ripple effects on all the smaller related rules. Like a small cog in a great machine, its removal can result in the whole system malfunctioning.
D20 D&D players who min-max often operate on a different wavelength in games than folks who choose options based on the value of how cool it sounds on the surface. In some cases, a min-maxer player might see one PC who's going to end up becoming a drain on party resources, or who is adamant on sticking to an underpowered option.
Combined with the earlier druid story and the Stormwind Fallacy being a frequent attitude in some gaming circles, min-maxers can often feel attacked for their play-style or feel as though they're part of a different fandom entirely from fellow D&D players. It's unfortunate, then, that some min-maxing communities end up taking a hostile attitude towards others. In some cases it may go so far as to dictating how other players should build their PCs, creating an overpowered PC to prove some point against the DM and/or gaming group. In worst-case scenarios they might go as far as to assume that their encyclopedic knowledge of build combinations and rules exploits makes them an intellectual ubermensch amid a sea of idiots who just want to game without worrying so much over builds and balance. Frank Trollman and his fanbase among the Gaming Den are a good example of these previous attitudes, and their attitude for starting flame wars on other boards (including Pathfinder's open playtest) has helped contribute to said negative attitudes simply by being the loudest and most negative voices.
A Personal Conclusion
The odd thing is I consider myself a min-maxer, but when it comes to actual games I don't always have the time or resources to build PCs and encounters to such rigorous positions. As a DM I often wing it or shift around monster attributes or reskin existing enemies to make for a challenging fight which doesn't become a curbstomp battle. Sometimes I pick sub-optimal choices deliberately for NPCs, and I've moreso relied upon the advice of other CharOps folks for PC building than trying to do the work required myself. In spite of agreeing with a lot of their positions I don't really play as one very often.
I do think that hanging out among min-maxers for years has helped me become better as a gamer, and has helped D20 D&D in several ways. You see, in spite of being very critical of the many flaws of 3rd Edition D&D and its D20 spin-offs, min-maxing communities still enjoy and play the game and find ways to change or work around said flaws.
3rd Edition D&D is one of the most imbalanced Editions on the market.
Its inclusion of trap options "to reward system mastery" is a terrible idea.
Roughly 50% of the games' levels see a dynamic shift in how the core of the game is played, and the prep time of the DM goes up exponentially as they have to patch problems the playtesters never discovered or touched.
I can hold all these opinions, but I can still love this game in spite of its flaws. Their knowledge of the rules means that min-maxers are very good at being critical of their own game and still loving it. This is a good tool which can help one avoid the adopting the more obsequious behavior in the tabletop fandom: things like "Strength caps for women are NOT sexist! Otherwise you're calling Gary Gygax sexist!" or "People who are unhappy with this latest bit of errata should stop complaining and play another game". I think that the willingness towards relentless self-criticism of one's own games is a much more valuable lesson than all the Handbooks and class guides put together. Without it, so much more of the D&D fandom would remain stagnant and unwilling to change, willfully blind to its own flaws in fear of losing the love they have for their own game.
PS JaronK's tier system for classes is another good read, examining game balance between classes (or more so the lack of it). It's a great thing to show to D20 newbies, and this post examines how the various classes interact with each other.