Quote - @lesbentley: as an extreme example, imagine someone playing with a hula hoop. The hip moves about (a lot), whereas the rest of the body stays pretty much stationary. You can't do that why a figure in which the hip is at the root of the hierarchy. And there are lots and lots of poses like this. Imagine a woman in high heels walking, with her hips swinging all Marilyn Monroe style. In a traditional figure, you'd apply a y rotation to the hip and then not only adjust the thighs to compensate, but also the abdomen. With the way Antonia is rigged, you might even be able to use IK on the legs and then only swing the hip2 actor to get the desired effect.

This is very interesting to me, as I've just spent a lot of time keyframing the millenium horse for a walk, trot, and gallop. I did a lot of pelvis rotation with compensation in the thighs and abdomen.  I want to re-rig the horse figure, it drives me nuts.