They are mainly social clubs, but I think some of them participate as a group in community events. It's all personal preference, but I'd rather be in a club that was related to my interests or what I was studying.
I agree with Jarrah. I would rather belong to something that pertains to my major. However, it is my understanding that if you are into partying, then a fraternity or sorority is where you need to be. I'm sure there have been some good experiences come out of belonging. Surely someone can enlighten us.