We work the horses hind legs forward to the point in which they can best support the lift of the horse’s chest. It’s not about bringing it forward as much as possible, or making it cross as much as possible (for example in the half-pass).
When the hind legs step over the correct point of mass, the joints become stiff and don’t bend, and with a too strong crossing, the hoof doesn’t get into the ground straight anymore but first with the outside hoof wall. Moreover, unhealthy sheer forces can ruin the joints.
So what is important is finding the point where the power can flow clean through all the joints and where the stepping under gives the spine the correct shape. You can see and feel it as correct rotation (inside hip and ribcage lowered), and the withers being lifted out of the shoulder blades.
More is not always better