An absolute must for workouts. Over time, after lots of repetitions our muscles start anticipating the movement. It's actually funny for me:
I've got used to certain music, that I may not ordinarily listen to, in my Spinning classes.
Here is an example:
Hearing this on my Ipod will make me burst into a sprint, quite spontaneously. Not necessarily a good thing when you are trying to keep an even pace during a race :)