Sharath spoke about each of the 6 classic yogic cleansing practices and concluded that Ashtanga practice achieves the same benefits and thus largely replaces these practices.
Balancing in a full squatting position is one of the most important and challenging aspects to this posture. The feet are your foundation, they are directly in contact with the earth.
Often I'm trying to create a new pattern where an old, rutted pattern exists. And the chances of that rutted pattern continuing are great and so to create a new pattern takes a total investment from the student and I have to have that agreement.