IMHO ATG squats are overall better for you than parallel. I think taking any movement through its entirity is more beneficial than doing partial reps, which a parallel squat, again IMO, is.
I dont stop the bar 3-4 inches above my chest on bench and dont do quater reps on curls etc etc so why do it on squats.
Plus the hamstrings get involved when I go past parallel and recruiting more muscles cant be bad, cant it?
I think there is also a lot of presure put on the knee to reverse the movement at parallel, rather than taking the move to, what I feel, is the natural conclusion.
Children dont parallel squat when they pick things up, the go ATG, and that is a natural movement.
Who can do them... I think anyone with enough flexibility, my Mrs CANT squat down without her heels coming off the floor, but Im sure a pair of Oly shoes whould sort that out... If she ever decided she wants to do some squats that it