It is a way to show how much of a douche bag you are. Facebook noobs are known to go crazy with a whole bunch of random, pointless, and meaningless applications installed on the profile. But the usage of facebook applications usually die down for most people.
There are only a few good, clean, fun Facebook Applications in existence, without ads, without spam, and without invites.
Joey: You know Ross has like 100 random Facebook Applications installed on his profile.
Rachel: Yea, he's such a douche bag.
Joey: Was I once like that, when I started Facebook.
Rachel: We all were like that at some point in time.
Joey: The only Facebook Applications I use are the clean ones, like gaming applications.
Rachel: Me too, by the way, I beat your score at Tetris.