From this set-up it's easy to make a great shoulder turn. First, his right knee is stable and supporting his backswing. Notice that both arms extend away from his body, unlike most amateurs who keep their right arm too close to the side. He used to reach the top with the face closed, which created a lower than optimal shot trajectory. He understands that no one has ever hit a shot in the first half of their downswing.
Many golfers rush the downswing, throwing off the timing between the upper and lower body.
The most important key to a great swing is learning to coordinate the body turn with the arm rotation. Rushing the backswing or the beginning of the downswing destroys the proper blending of the two. Because his body continues to rotate, Sutton is able to accelerate the clubhead well past impact. This is vital for producing consistent clubhead speed shot to shot. This focus on acceleration is something that Jackie Burke Jr. helped Sutton develop.