I've been thinking lately about the prevalent notion of "skiing tall" at epicski. Skiing tall, to me, conjures an image of someone with both legs fully extended throughout most of their turns - not what I want my learners to do when skiing. What I do want to see, starting at the transition, is flexing the joints and flattening the skis as we enter the new turn, progressively engaging the edges to form a platform, then extending as the platform is created. But again, not "standing tall", as we're never fully extended in both legs.
My thought on skiing "tall", i.e. fully extended, is it blocks our skiers from being able to circumduct or pivot as effectively as they could with some flexion, and it becomes harder for our skiers to move their feet fore/aft or manage pressure.
For example, check out JF Beaulieu's skiing below:
At transition, check out the flex through JF's joints:
And then check out the still visible amount of flexion in his hip/knee/ankle when he's most extended:
So the idea of "standing tall" doesn't really fit, for me, as good general advice. Perhaps situationally it's good for skiers who are squatting and consistently releasing all pressure from their skis, or as part of an exercise for folks who can't seem to get out of the backseat, or to help skiers who need to drive the skis as bit more forward through powder--but it's probably not the general image I'd want to create for my skiers. If anything, I'd want to give them an image of flexing as we transition, and extending laterally, the skis looking like a pendulum arcing from side to side under the CoM.