I can understand the need for chairs. For example, if you go to a show like Testament there will be some older metal fans there, often with their wives, and they don't want to deal with the young bucks running circles around them.
It is also nice to have a place to sit other than the floor if you get kicked in the head. Happens to me a lot with crowd surfers who for some reason wear combat boots to shows. When I see them coming, I usually grab them by the belt and drag them to the floor. Call me an ass, but immature little brats who flail about like fish out of water deserve it. They need to learn how to crowd surf properly.
Edit: my bad for continuing off-topic, so [ame]http://www.youtube.com/watch?v=X8_mN0ihhQA&NR=1[/ame]