One of the big debates in the world of golf instruction has to do with the topic of the swing plane and whether people should employ a one-plane or a two-plane swing. I don't currently know enough to answer that question, but I do see something interesting and relevant in Ben Hogan's swing.
When I look at Ben Hogan's swing, I see two distinct planes.
The first plane, which is the plane of the backswing, is set by his front arm and is roughly in the plane his shoulders.
The second plane, which is the plane of the downswing, is set by his back arm and is much lower because it essentially runs from his back hip through the ball.
This is relevant and important because many people, including Tiger Woods, believe that golfers should swing in one plane; that the backswing and downswing should occur in the same plane.
However, that is plainly not what Ben Hogan did.