The way Sigung Steve described it to me, is that you pivot on every part of each foot. Imagine the combinations! One of our math experts could probably tell you; but bottom-line is that you meticulously and deliberately explore every option available.
To simply things for me, he said; "inside, outside, heel and toe. That's four. Add the second foot and you're exploring an exponential universe of possibility in only one overt movement." And each one has its potential application, considering the chaos of combat.
I recall Sigung telling me that Guru Ted Garcia once said, "That's not a movement, that's a thousand movements." It's true. In each movement, stance, technique there are a thousand elements that comprise the whole, and for each practitioner those thousand elements are just a wee bit different, in order to compensate for age, injuries, size, weight, previous training, attitude, emotion, health, agility and a multitude of factors that enter in to everything we do everyday.
That's why it's called a "Martial LifeStyle."

Peace,
Art