MUSCLE MEMORY DOES NOT MEAN YOU KNOW THE PIECE.This is an awful way to memorize your pieces. Not only should you have muscle memory, but auditory memory as well. You need to remember how the piece goes, hear it in your head. Also you need to remember how to produce the sound that you want to create. When you perform, you can't just let your hands do all the work. You need to listen to your own sound and consciously think about HOW you are playing these notes. Fingerings should be automatic yes, but this is NOT the only thing required for performance.