Some world class performers slip into the habit of adopting a number of unnecessary movements (mannerisms) when playing the organ.
In organ playing, there's an old dictum which says "all unnecessary movement is harmful because it's a waste of time and effort."
This holds true and can be applied in a wide variety of applications in life, not just organ playing (photo).
Organ playing requires no physical strain, nor does it require a litany of mannerisms.
When we see performers swaying on the bench as they play, shaking their heads as if they were trying to paint a fence with a brush between their teeth, crunching their entire body over the keys, raising one hand high at the end of each phrase, rapidly flipping their hands upward when releasing final chords as if they just touched a hot stove, sometimes even throwing their hands three feet into the air when the piece concludes, rotating their elbows rhythmically like they're trying to do the breast stroke, bobbing their heads and grimacing as if they were in a trance, etc., it's important to realize that none of these mannerisms have any effect on tone production [See blog, Bach d minor, Part III].
They do it either because they have themselves convinced that can't play the organ any other way or to make people who are watching them think that they're in communion with something esoteric and are actually doing something.
The grandmother in the back row and the little boy in the front row who are downstairs listening don't care if the organist is sitting up straight, bobbing their head, making faces, chewing gum, rolling their eyes, slobbering at the mouth, waving with one hand, or swaying on the bench like a drunken sailor; all they expect is to hear some organ music, to hear it clearly, and to be moved by it [See blog, Touch, Part V].
Mannerisms in organ playing impress only those who listen with their eyes.