The up move was used for unweighting the skis with old skis by people who wanted to pivot or skid the old skis. The reason it was used was because it was easier to pivot an unweighted ski. The typical move was for that purpose was to unweight the skis and pivot them enough to get them across the line of travel enough so that a skidded turn in the other direction would be easy to modulate. What I am pointing out is that there was an alternative to pivoting the ski, even back in the stone age, the alternative was arc to arc carving that involved keeping your edges engaged, and merely replacing the left edges with the right edges without any pivoting of the ski. This was accomplished by untipping the skis to decrease the radius of the old turn enough that the slight release from a very long radius turn to straight mattered not at all, and then tipping onto the new edges with a decambered ski to engaged the new edges, just like it is now.
Good posting Ghost. This is a very good description of why we had to up-unweight to turn. Sure there was an alternative, in fact there were and still are quite a few. Carving was and is one of them. A wedge turn is annother. When you do a wedge turn you dont need to unweight your skis. They are alredy skidding at an angle.
This is important. When teaching students how to wedge turn some instructors try to introduce the up-move because it will come in handy later when the students learn to turn parallel by up-unweighting (skidded turns). However, later when they learn to carve they need to un-learn the up-move since its not needed and its bad in carving. This is the reason I teach students to wedge without up-move since its not needed and its bad. Skis are allready skidding on BTEdges. Only thing you need to do is to distribute your weight and manage the pressure and you are turning. And when you start to carve you just go faster and along the edges insted of slightly at angle. No turning of skis, no up-unweighting no pivotting no skidding. Just edge locked fast carving. However, the students do not learn how to up-unweight and turn parallel. They will struggle in bumps and in powder and varying snow conditions. They will also have a problem skiing very steep slopes and narrow shutes. Thats why you need to teach students different techniques. Typically at different ages and levels. Lesson learned, for good all mountain skills you need to be able to use different ways of turning.