When riding flat bindings, you need to be in the neutral (reference) stance, with no twist in the upper body to keep the board from twisting.
As you twist the upper body into the fall line, the rear heel will lift (as the back knee bends more, and the front knee straightens out more), along with (however less noticable) a lifting of the front toe. When strapped into to binding, These pressures will put twist into the board. By building the lift into the bindings, the rider can assume that same postion, while taking the twist out of the board.
AASI is promoting riding in the referece stance, utilizing counterroatation and board twist as needed, allowing a rider to have maximum range of motion available for corrections and adjustments requiring upper body seperation. another advantage of riding flat (toe to heel) is the knees and ankles will flex equally, allowing better pressure control along the edge of the board.
These points are particularly applicable for freeride/freestyle riding (as in using the CATEK Freeride), However should also be considered and discussed among the alpine set as well.