Why tennis players pick and choose from different balls?

Question

I can’t find any real explanation for this. Are there different balls? Some harder, some faster… or is it just a habit from players?

In: 56

Answer 1

I always pick the ball with the least fuzz for my first serve (which I hit hard and with limited spin) and the more fuzzy ball for my second serve (which I hit with a lot more topspin).