Taking into account the force balance required to preferentially weight the front (or rear) of a tipped ski while maintaining vertical equilibrium, it would be very difficult to distinguish "steering" effort from simply maintaining that weight differential with a tipped ski. They both put the same torque on the leg. There is no movement in the case of hardpack or ice, but there will be some movement in deep 3-d snow. Just sayin'.
I hardly use any steering at all as it is defined by Rick. For years I was happy carving edge-locked SG turns (even before we had such a thing as a SG race), and when the situation demanded, carving non-edge-locked turns by bending the ski with forward weight distribution before tipping and forcing the ski into too tight a bend to make an edge-locked carve, but I gave up on manually turning the skis for most purposes a few decades ago. About half a dozen years ago I decided that edge-locked SG turns might not be the best approach to tight icy moguls and investigated "steering". I eventually decided that skidding with tipping and for-aft weight distribution and pressure control was just easier on my knees than steering. I still suck at bumps though, so maybe it's because I don't steer in the bumps. I will steer occasionally, though very rarely. About the only time I can recall is when coming into the lift line on very flat skis once in a while, and even then I mostly prefer to let the snow do the work.
I find turning the feet to be usefull in bumps and in powder. And in the park since there you have to suddenly change were you are going and you twist your skis sideways when railing and in the half pipe at the lip you need to turn back down again. But Im also not consiously steering when I ski normally since I try to carve most of the time. Note that its hard to distiqunishe between what is turing your feet and what is not especially if you are not aware of the movements involved. Unweighting, unwinding and hip rotation kind of blends in.
BTW, does turing the feet in the air qualify as steering?