We teach to turn the head away on the ikkyo, nikkyo and sankyo pins, primarily because of the nikkyo and sankyo pins. On those two pins, Nage usually places his knees against the ribcage and very close to the head. Turning the face away saves teeth and noses in training. We turn the head for ikkyo just for consistency.
Agreed. Also, as in kotegaishe, in case disarming from a tanto or other weapon is sloppy and it accidentally falls, better it falls an arm's length to the side of one's head rather than on one's face.