A few observations on being forward, and forward pressure on the boot cuffs for ski racers, and when you don't do it:
1. To arc your skis to carve a tighter turn more cleanly (and thus go faster than your competitors), you must apply forward pressure early in the turn to create a larger bend in the ski forebody, which creates a tighter arced turn.
2. This is not simply "not being in the back seat" but is (especially in slalom) aggressive leveraging, with hips and center of mass forward at turn initiation. See descriptions, from a PSIA 3 intstructor/Nastar 10 handicapper who went on to improve to become a masters racer ("'Forward' in slalom means leveraging, not pressuring, not feeling your toes press down on the foot bed. 'Forward' means reaching past the tip of your skis, positioning your torso over your toes if you want to make the gate.") here:http://www.psia.org/psia_2002/educat...ersprogram.asp
Carolyn Lalive says of slalom, "There is plenty of aggressive flex in my knees and my ankles. We need this kind of forward pressure on the ski's tip to get it to come around." at:http://www.skimag.com/skimag/turning...326207,00.html
Other racers make similar points about GS and even downhill:http://www.skimag.com/skimag/turning...326091,00.html
3. For ski racers, you stay forward well into the middle of the turn, and try to pressure _both_ boot cuffs not just the boot cuff of the outside ski (e.g., minimize fore and aft divergence, avoiding substantially leading with the inside ski, during turn initiation and the steering phase of the turn.)
4. One tactical exception is where there is an abrupt change from steep to flat, where the dishing out has a tendency to throw you forward. If you're way forward before that, getting thrown more forward can leave you out of balance. (I should have such problems of being too far forward in the steepest part of the course...)
5. For non-racers, a second exception would be skiing things like cut up heavy wet fresh snow (euphemistically called Sierra cement where I ski), which is over the top of a layer of ice, as you're constantly being thrown forward as you hit the heavy gloppy stuff, so you should not start your turns in an exaggerated forward position. Probably people who do cliff jumping into powder should avoid being too far forward as well, which is why Atomic's adjustable binding positions (assuming, probably incorrectly, that most of us don't simply react to pushing the bindings forward by sinking our butts down and back) have "racing" as the forward position, "all around" as the middle position, and "extreme" as the position toward the tail of the ski.