Starting at Stride 2, the flat locomotive state is
built on toppling off a long leg, using the inside edge of that long leg as support. One then lands on the outside edge of the short leg's foot, recenters the upper body while extending the short leg into the new support leg.
And, once one has a parallel turn, one can easily, on flat ground, learn to convert the parallel turn into a linked series of either locomotive or braking manoeuvers. By managing extension and pressure.
Useful?
you tell me, I expect you know more about skiing than I do. It's certainly excellent primary muscle conditioning, with very little chance of building imbalanced kinetic chains. And it's far better than cycling for adductor, abductor, hip rotator conditioning.
I also contend that anyone with a will and skiing-level coordination can progress to this level in the space of one summer. If they don't...well, that's kind of like talking about skiers permanently plateaued at L4.5, no?