A lot of great golfers start their swing with someting. jack pushed his head back. Player pushe his right leg in. Ernie has a forward press and so Tiger has a slight forward press also. I am a 4 handicap why do they do this if I were to do any of these things how would it help or would it not help at all.
Most who do the forward press do so to start the backswing with a straight left wrist. I do this because it helps prevent me from rolling the wrists prematurely on the backswing.
Most who kick the right leg in do it so they are conscious of having proper weight balance – you can't sway to the right with the right leg kicked in.
Jack turns his head so he establishes left eye dominance during the swing – not sure why this is better, but it helped him (and Lorena Ochoa). Also it seems like it would help with keeping the turn unrestricted.
Really, they all do it because they feel comfortable with it, and it is part of their routine. Watch the pros – the exact same pre-shot routine every time. Tiger even takes the same amount of time for each shot +/- a second or two.
So, I guess the moral of the story is to do what feels like it helps you and do it the same way every time.