I go ass to the grass every time, but odds are the guy next to you in the power rack is not. Odds are he's not even going to get his knees to bend.

I go down like a cheerleader on prom nite.

flexibility
not sitting back
hips not worked
unable to go that deep because maybe of some body problem (genetic, bones, muscles..blah blah blah)
urban belief of ruining your knee/hips when going ATG

i do know that it is required and a must to go ATG on squats, though it is not easy or near impossible for some. this could be replaced with box squats till they learn.

i go atg in every squats. i experiment with it though, sometimes below parallel or just parallel itself.

yes

i break parallel everytime, despite the fucks who load eight plates on the bar and go half-way down.