Even though they do make money off of them (how volunteer assistant coaches get paid), "Prospect" camps are a useful recruiting tool that coaches use. Most of the time they put a limit on the number of players that can sign up and many of them are those that the coaches invited or players that have been recommended to them through "middlemen". Camps give coaches a way to interact with the kids and control the situation they are watching them in, which they cannot do in the traditional way of just going to a tournament or showcase and watching from the sidelines. They are expensive usually though, so as one of the previous posters mentioned, it makes the most sense to only attend them at schools you are interested in attending.