Point. But for the most part, you're going to be focusing on a school or two - maybe three, if you're a Swordsage - simply because of the slow gain progression for maneuvers known. Take your Warblade. Warblades gain a known maneuver every odd level (thereabouts - it actually gains one at 2nd level, but that's the only time it will). So, basically, you get 1 new maneuver with each new level of maneuvers that you can gain access to.
Given that Warblades get access to Iron Heart, and the discipline contains a ton of moves that are powerful and useful, you'll probably take most of those new moves from Iron Heart, unless there aren't any maneuvers you consider worth taking from that tier. Which, depending on what you want to do, I could personally see there being a few tiers you pick another move from.
For Warblades, Diamond Mind and White Raven are usually good secondary disciplines - partly because each offers some useful abilities, and partly because those two share an associated weapon (bastard sword for Diamond Mind and longsword for White Raven).
Swordsages have the ability to diversify, because they gain a new move every level, going up to 25 by the time they max out (compared to 13 or 14 for Warblades and Crusaders). But even then, you're going to want to limit yourself to no more than 3 disciplines, because the requirements for taking higher-tier maneuvers require you to know a certain amount of moves from that discipline already.
For example, the Dancing Mongoose boost from Tiger Claw is considered good because it lets you make an additional attack action at your full attack bonus with each weapon you wield, up to 2 extra. So for someone with Two-Weapon Fighting, and its advanced variants, this is pretty damn awesome. However, this requires you to already know 2 Tiger Claw maneuvers to learn. The Raging Mongoose boost is even better, letting you dish out double that of Dancing Mongoose, at a cost of 3 Tiger Claw maneuvers.
Given that you can only add 2 moves per tier you gain (since you go up 1 tier every 2 levels, if you're straight single-classing Swordsage), focusing on more than 3 disciplines at a time means you end up pretty spread out. You can get around this somewhat with the fact that starting at 4th level, you can swap out any one move you know for another one up to your highest level, but you still have to abide by the learning prerequisites.
Plus, given how Martial Study and Martial Stance work, you're either going to need to play a Swordsage, or PrC into a class that'll give you access to maneuver schools you lack. Warblades can manage to gain access to all 9 schools, but it requires PrCing along one of two paths - the Master of Nine is the quickest route, but you can also accomplish it through combining the Jade Phoenix Mage PrC with either using a couple of feats to be able to jump into Shadow Sun Ninja, or using Ruby Knight Vindicator as a springboard into it.
And it's quite simply impossible for a Crusader to do it.