3 points: 1, Rooting, as wab25 said, is important since the power of impact, especially in a straight punch, is braced by the solid rear leg and keeps the force (kind of like a rebound) going where you want it to. Kata teaches good habits. Once mastered, it is possible to punch hard without the rear heel planted using other body mechanics. 2. Kata is not fighting (sort of), but neither is light contact tournament competition. Bringing the heel up increases range a few inches to allow a point hit, even though the punch may leave you off balance, not have full power, etc. that many judges nowadays may not consider. 3. Rooting helps keep control of your weight, important in grappling, locking and take downs. By the way, Acronym, which advanced katas do you know?