A few days ago, there was a performance by a pianist (American?) who quite clearly knew and loved the piece. It was easy to tell from his facial expression, his movements, his timings. Unfortunately, this entirely distracted him from the performance, and he failed to communicate to the audience the sounds and ideas he was hearing in his head. The movement distracted me also; I did not particularly enjoy his performance. The pianist who followed him loved some passages and was extremely competent in the rest; this also showed in her playing in that she played some passages with love and others merely with extreme competence.
Anne McCaffrey said in "Dragonsinger" that "Petiron abhorred a musician who had to use unnecessary body motion to keep a rhythm going." She had good reason to make this comment.
I had a thesis to follow this argument, but as I wrote it, I discovered a new and better thesis in the argument itself. Therefore I will post only the argument.