Well analyzed and said. Just one more benefit about rotation, that would reduce the resisttance! This is aginst the old fashioned belief that rotation would increase friction, hence resistence. Just imagine to youself that a flat body on the ground, and draw two parallel lines along your two stretch hands. This area would be seen as the reistance, and our aim would be to reduce it. Now, if you rotate in your swim, your body would slightly tilt upwards and sidewards, to one side. Thus, the width between the two lines, would be reduced, hence relatively a smaller area. It follows with smaller friction, and hence too small resistance. Hope I may present to you that rotation also reduce resistance, hence good for forward movement in our swim.