I Just Posted This To A Forum (and thought it was worth sharing...)

Full Squats = High Bar Position
I've mentioned this many times to many people and apparently people either don't agree or understand it, but here goes one more time...

If you are doing "full" squats (atg, ata, etc) then, preferably, you should be using a high bar position. At the very bottom of the hole, the hips move forward to achieve full flexion and if you are using a low bar placement, then the back must flex to keep the bar's center of gravity over your foot.

Long story short (IMHO):
*Low bar position = parallel or below parallel, hips move back
*High bar position = full squat, hips move vertically

Related Posts:
Squatting and Lower Back Pain (Part I)
Squat Rx #21 ("Hips Back")