if your talking about coaxials. no more then a 2 way is needed. 2 ways have the woofer and a tweeter mounted in the center. that covers your midrange/mid bass and highs.
3 and 4+ ways are pretty much marketing gimics. they add in a crappy "mid range" driver or a "super tweeter" to make you think it'll sound "super", lol. don't waste any more money for a 3-4+ way vs. a 2 way.
with components, a 2 way is the same thing, but the woofer and tweeters are seperate and they have higher quality external crossover boxes instead of simple capacitors. 3 ways give you an actual mid range, tweeters and mid bass with a external crossover box too. most people will say that you won't notice a difference between a 2 and 3 way component set.