In skiing and action sports, balance is not a static notion, as it would be balancing on top of a ball, but a very much dynamic notion. In fact, we maintain dynamic balance through athletic movement.
Dynamic balance includes anticipating the movements required in the near future and possibly compensating ahead of time, using the momentum and inertia of different parts of the body to leverage against etc... if you want more theory, look into kinetics and dynamics, but let's look at dynamic balance specifically for skiing, and how balance is created by good movements.
Static balance is maintaining a balanced position, for instance as we glide down on a green run or in the middle of a long, slow turn of constant radius, where we balance our mass over the base of support / ski.
Dynamics and kinetics deal with the movement subject to external forces, like gravity, snow reaction etc. When we ski, especially on a given trajectory, we do much more than what we consider static balance to be, for instance we use and create forces, like creating GRF by putting the skis on edge and engaging, using the long leg to brace against it, stacked body to balance and resist it briefly to get deflection and create a turn. In the mean time, we allow different body parts to move in anticipation of the next apex etc.
This is where good movements create good balance.
For instance, foot tipping and carving. These activate the kinetic chain from the bottom up and create a stable platform that we can balance on when the GRF grows. By contrast, pushing the skis away from under the hips more often than not impairs balance - imagine sliding on ice and pushing yout feet away! Would you feel balanced?
Other aspects, very important are how we deal with external factors like 3D terrain for instance, where external random forces appear all the time, as we hit a bump or cross-rut etc.
The static balance principles of balancing COM over BOS work well for standing still or slow skiing, but you can see why in high performance skiing, it becomes largely irrelevant, although the basic principles still apply: we still want to balance against the forces and line up the body with the forces to some extent, but we are more concerned with creating these forces and using them, never quite balancing enough to become static, always leaving some imbalance to allow and direct movement.
At this point we can talk of balance as being an outcome of effective movements. There are ineffective movements and actions, which impair and reduce balance, while effective movements at the right time, create balance or at least create a chance to ski balanced, from apex to apex.
While we've seen some positive examples above, some negative examples would be:
We work on developing dynamic balance not just to prepare for the beginning of the season, but throughout the season as well:
Here's an example of lane changes: