Feat chains allow things like GWM PAM Sentinel etc while making a build with all or most of those difficult enough to not be much of an issue till it's a level appropriate combo.And you triggered my trap card. I have a serious problem with Feat chains in 3.5 and the effect on the Fighter on Feat design in general. And while this isn't the thread for this derail, I'm not about to make a new thread on the topic 20 years later, so here we go.
So Feat chains are terrible. Why? Because you're forced to take a lot of Feats you normally would not in order to eventually get something good. There's unnecessary bloat, and the Fighter is the reason. Because the Fighter gets extra feats, anything good that you want to be a Fighter exclusive is locked behind a bunch of Feats that, frankly, are terrible. Let's start with the poster child, Whirlwind Attack.
So we start this chain with Combat Expertise, a generally pointless Feat. It's an improved version of fighting defensively (sort of) that requires you to have a BAB of 5 to get the full benefit of, by taking a -5 to hit (as opposed to the -4/+2...or +3 with 5 ranks of Tumbling you get from Fighting Defensively). Given the way iterative attacks work, this is really only useful if you're making a single attack in most circumstances. And rather than being an upgrade to fighting defensively, it's its own mechanic which could stack with fighting defensively?
Oh and it's the cornerstone of a lot of feat chains that (like Whirlwind) have nothing whatsoever to do with it's benefit. Like, say, improved combat maneuvers. And you need a 13 Intelligence on your Fighter or you'll be locked out of most feat chains.
Next we have Dodge. Need a 13 Dex for a situational +1 to AC. Wow, be still my heart. Next, Mobility, a Feat that gives you a +4 bonus to AC when you do something you shouldn't be doing, that is, giving enemies a free hit. I can't tell you how many times I provoked with mobility and the DM rolled a 20, lol.
But wait! With a BAB of 4+ now you can get Spring Attack, a feat that lets you make a single attack and dash...err...slowly walk away! It's not useless, as you can use it to get inside superior reach and not need to rely on Mobility, or avoid taking a full attack, but unless you get some serious speed, it's usually just turning a fight from "stand still and trade full attacks" to "move and trade single attacks".
Then from here, we get the super amazing ability to attack everyone adjacent to you one time. A Human Fighter can pull this off by level 6. Any other class? Well a Human Barbarian could get it by level 9. Non-Human? Level 12.
Whirlwind Attack is not a level 12 ability. But thanks to the Fighter, it technically is. Most classes are so Feat-starved that they can master one Feat chain before the game ends.
And then, as if that wasn't bad enough, books like the PHB2 add more top end Feats to make sure that a Fighter never masters a Feat chain, because it just gets more links! Double Strike, Karmic Strike, Robilar's Gambit, Combat Reflexes builds so you can, by top level, get the super amazing ability to attack twice whenever someone provokes from you, which they do by having the nerve to attack you in melee...all while Barbarians are charging for 300 damage and everyone else is just not attacking you in melee and using spells or ranged attacks.
Of course, all this did was make sure that if you really wanted to get the most mileage out of feat chains you just played a human, dipped 2 levels of fighter (or Feat Rogue from UA or both) and acquired the abilities of some other class to make them really shine.