When a ball is broken or cracked in a match, professional players try out the new ball by having a knock up before continuing play. Is this really necessary as during some tournaments such as T2 several balls are used. A new ball is thrown to the server rather than fetching the ball after a smash. This is done to speed up the game and make it better for spectators (and youTube) but players cannot try out each ball-even at game point.

Do professional players really need to try out a new ball and can they feel different or is this just for their own feelings?