Cosplay events are usually at a convention of anime or comics or whatever, and there are all sorts of booths, movies, and activities to engage in. My friends are in a cosplay group and they preform skits and have a blast doing it.
What does a person get out of it? Enjoyment, same as anything else. What does a person get out of skateboarding? Just a bunch of bruises? Nope, they have a fun time doing it, and that's all that matters.
I'd post pictures of my friends, but they havent done any FF cosplay. They've made some amazing costumes though.