A sense of balance must be developed above all other skills, for great skiing to be possible. In dynamic skiing however, we talk about stability with mobility, as the notions of stability and balance must accompany mobility and dynamic movement, this is the realm where balance is an outcome rather than an input.
The notion of balance, while requiring reaction and compensatory movements to keep the body in balance, is in itself a static notion - basically meaning "can we maintain a pose":
In biomechanics, balance is an ability to maintain the line of gravity (vertical line from centre of mass) of a body within the base of support with minimal postural sway
While slow skiing on shallow runs, this type of balance may be of interest as we glide, but high-performance skiing is nothing but static and we never spend time "in balance" in any specific position.
Grinding the ski is not a focus in great skiing, so we prefer to focus on the notions of dynamic balance and the more advanced real balance, at the performance level. But first, let's start with the basics...
Here are some snippets from the article linked above:
The brain gets better and better at sending a motor program for a specific movement, each time the body performs the movement. If the proper motor program (ie- the proper movement) has been practiced you’ll get better at that movement skill.
So what if the motor program (and movement) is wrong--- Like that consistent slice you have in golf? Then your brain gets better at sending the wrong motor program. This is seen all the time in athletics. It's why coaches work so hard at getting their athletes to practice proper form.
Read We ski with the feet and ankles for more on how this applies to skiing and why it is critical that good skiers focus on using their feet.
There are many sensors in the soles of the feet, which we use to feel balance and, if the feet are cold, these sensors don't function as effectively. Also, the muscles' response times are reduced, when we need to react to balance changes.
If the boots are too wide or too big, then certainly the feet are sloshing inside without a good feel of whatever is outside the boot. Also, any small corrections we'd take to restore balance will not be effective, because they would not be transmitted through the boot as quickly as with a properly fitted boot.
On the other hand, if the boot is too tight and cramped up, that will also impair the feeling for balance. Also, the range of motion available for balance correction is reduced. This is one of the reasons why properly fitted boots are paramount for good skiing and good footbeds, that don't take too much room inside the boot and which support the foot just enough but not more than needed.
What's more, improper ramp angles may impair fore/aft balance in mysterious ways, so using a good knowledgeable boot fitter is a must. Ask yours next time what ramp angles you should use (it's rather a trick question).
If your workouts consistently include unstable surfaces such as wobble boards, balance mats, balance stones, exercise balls, bosu balls, skate boards, slide boards, etc… you will become a better balancer.
These kinesthetic skills will cross over into the sporting environment, allowing your body to adapt and adjust to the movements you demand with greater efficiency
Balance is created by sensing when we get out of balance and then reacting to restore balance, with dynamic movement. Range of movement, strength and agility for recoveries are critical skills, so keep in shape! Core strength is especially important, as we have to move the upper body by leveraging the feet.
Banking will impair balance by reducing the range of motion available for recovery as well as, usually, creating some unwanted momentum in the upper body.
Training balance off the snow is a must! There are many related sports that develop balance and it can be part of a workout program by including balance boards, Bosu balls and other.
Balance must be developed on snow as well, to learn and engrain proprioceptive reactions to typical skiing situations, as challenging and increasing ranges of movement.