Federer won several slams very convincingly, if I'm not mistaken, without a coach. Surely someone who is the greatest player of all time would know the game better than anyone else...or am I missing something? Maybe his coach is there because he doesn't have time to arrange courts or other time consuming stuff? That would be reasonable. But in terms of his actual tennis, I don't see how a coach would help when he won many slams without one.