Now with computer voice recognition (As Dragon Speak..ect) , you can now use your own voice, or sound effects with your voice instead of a mouse.
You would say...."swing" (or something, and then..."stop" when the swing meter gets to the impact bar. You could download any word cue or sound effect to make it work; you could make that farmiliar clucking sound (when you force your tounge down from the roof of your mouth down to the bottom)..."cluck"....as a way to indicate you want to swing meter to stop.
Anyway, not everyone is capable of using a mouse due to physical handicaps, so they are using their voice to play the game.