Hip rotation can be using to improve range of most in the legs in a specific direction. In carving, this is useful to help twist the back half of the snowboard to a higher edge angle that the front at the last half of a carved turn. In my avatar pic(I'm in a duckstance, soft boots,), my hips are rotated toward the nose to give me more room to drive my back knee towards the snow. This has the effect of tightening up the turn towards the finish and puts an nice exclamation point on an already solid carve turn. For heelside, rotate the hips toward the tail to do the same thing. It's important that if you do this at the start of your turn it will totally hose up your turn. This move is only for the 2nd half of the turn when your edge set is solid.