Do you find extending/compressing actively throughout the turn decreases stability on hard conditions such as ice or when going beyond the speed envelope of a board and still trying to make it carve (it wants to lose an edge but you angulate and keep your center of mass so close to the board, you just muscle the edge into the snow)
Actively extending and compressing your lower body thoughtout a turn will usually increase stability in any condition because it's one of the best ways to manage edge pressure in a turn, especially as you move into the lower part of your turn. Compressing in the lower part of the turn can help keep edge pressure from increasing to the point of the edge breaking free and you landing on your butt. This is also true for when the terrain gets steeper.
It's also important to remember that like any other movement involved in snowboarding, actively changing leg length through your turn isn't always done through your maximum range of motion. Sometimes it's slight, subtle changes that make all the difference.
Also it's the timing of the move. In Brian's AWESOME toeside turn at 1:47, see how his CM starts wobbling to the inside and outside of the turn? That's due to Bryan gettins too extended too early in the turn.
I realize when keeping the COM close to the board, you naturally lose some ability to tilt the board up on edge, especially the heel side, (but I use aggressive forward angles like 48/42, so this is less of an issue).
I've never really found that to be an issue in lower angles(I right 18, -12). The trick to angulating on your heelside in lower angles is getting your butt below your knees
In my own experience, if I kept myself compressed (knees about 90 degree bent, but during a carve it feels like my ass is going to hit my boot), I get superior edge hold, and I still have room to down unweight aggressively. I'm still pushing against the board, but not in a way that my legs extend away from the board. I can ride different ways, but I have found the way I just described works best on ice and such.
But this is my own experience, if I'm wrong (snowwolf?) someone please correct me. Looking to improve my riding further this coming season.[/QUOTE]
IF you figure something out based on your own experience, you can't be wrong.