To hit the ball as far as possible and to not slice or hook, it is necessary that the clubface be square to the ball target (pathway) at contact. This requires excellent coordination of the body, arms and hands. Understand that any deviation of the clubface at contact, or more accurately, during contact of more than a few degrees, can easily send the ball way off course.
To ensure this accuracy many pros and high-level golfers, maintain that it is necessary to rotate the body correctly on the downswing. This is what will ensure proper club face contact with the ball which in turn, ensures accuracy of the shot. There is much to be said for the statement since body correct body rotation is extremely important. Without it would be impossible to have a good hit.
But even in the best body coordinated swings body rotation by itself is considered a “gross” movement as it involves relatively large muscles. Large muscles are not very good at performing fine skills as required for very accurate ball contact. Understand that if body rotation determines the position of the club face at contact, it rules out the role of the arms, wrists and hands which are controlled by much smaller muscles. These are needed for the fine aspects of the game.
If you closely examine the role of the arms and hands on a video tape of a good player, frame by frame, you will see that the arms play the most crucial role in establishing club face position. The arm rotation must be active in the downswing in order to reverse their actions in the backswing.
You would be unable to take a full backswing without turning the arms and consequently the club face. Nor would you be able to return the clubface to its initial position in the stance.
You can check this very easily. Simply take a half swing on the backswing and check in which direction the tip of the clubhead is pointed. If it is pointed up, as it should be, you have turned the arms. If it is still pointed forward, you did not rotate the arms or hands.
Thus, body rotation determines the club face at contact applies only when you take an extremely short backswing as, for example, when chipping for 10-20 yards or when putting.
For more information on the body, arm and wrist actions see Explosive Golf