Naaa not necessarily. It could be bit like dancing, you connect the mind with your body and strengthen the flow of communication between them. On the other hand, if its planned beforehand like "In that part I will do this and that" then it'll serve no real purpose but to act as a musician, and that's something you shouldn't need to act. If you would want express moods with your body as addition to the actual music, then trust your intuition and don't force it. Movement must come from inside, remember where the master of your body lies - This also guarantees that you will move accordingly to music, not vice versa, thus not distracting you from what really is the source of expression in that performance.
I'm not sure I agree with this. Of course I agree that movement should come from inside, and that it should be in accordance with the music.
But the thing about "trusting your intuition" on such movements seems suspect. What is good and proper and serving the purpose of music is often that which, at first may not seem natural at all if we're not used to it, and will not come from our intuition. Intuition is based on habits, many of which are often wrong.
Amateur pianists who have a habit of "moving" often think that they're "feeling the music", and that their movements are spontaneous and natural. But if you show them a video tape of it, they will often be appalled by how unnatural they look! And they will often find that when they eliminate such movement, they actually feel more natural than when they were moving.
So the only real way (in my opinion) to have free and spontaneous movement in performance is to eliminate all unnecessary movement in practice. If movement finds its way into your practice sessions, it may become ingrained and habitual rather than natural, and that's something you want to avoid.
- Saturn