They are there, as far as I understand, to deal with players contract renewals, to talk up and engineer moves for the players they represent and allow the player to get on with playing instead of negotiating contracts. In reality all they do is bump up transfer prices and wages to ensure they get a huge pay-off when they take their slice of any fees.
So the players employ them rather than the clubs in most cases I guess? Just another case of too much player power. Surely if agents are required than the should be vetted or controlled by an established governing body of some sort who can regulate their behaviour. Mind you I guess its all about money for them. I always cringe when I hear an agent say "I just want what's best for the player" yeah right they do