[BerntR]

Zack is very close to a one-planer on that film. Just a very small planeshift early in the down stroke. One plane doesn't require any steering of the club in the down stroke. You can aim at the ball all the way down.

Sean O'Hair has a very significant plane shift towards the elbow plane. The plane shift involves some steering and redirection of the club path, which is a disadvantage when seen in isolation.

I think the elbow plane has advantages too. Just not sure what they are exactly. There is something about the feeling of moving the club underneath the shoulder plane but I am not sure what it really is. Perhaps the right hand gets in a better position for driving with a lower plane.

Perhaps someone who really know TGM can fill in?