Later when discs appear so fast, you don't really have a choice to wait for them to be big, you just click on them whenever and wherever you can.
At the beginning at least it's not about speed, but you can wait it to be big and shoot for their center. This can give large point differences. This was intentional so a "little" strategy is put into the game. The early game will measure your rhythm and timing, and not particularly your speed.
After all I wanted this game to be easy but still fun and challenging. To not think just do it.. but still you have to concentrate on left and right buttons. Adding different discs would not bring more fun in my opinion. Although it might be a good idea to let it customized (but not being qualified for the score table of course).