oh yeah, with certain characters(buu, cell, krillin) once you go acend a level(button z), you cant decend back to your original form(button x). Decending is useful becuase when your in your super whatever mode, your exp amount gained is lower becuase of how high your pl is. Also, if you were to train in SS mode(im just gunna call it that now), you would only recive half or less of what you would recive in your normal form(why? becuase going SS mode multiplies your PL by either 1.5x or 2x, so when your in SS mode, your pl is 1.5x-2x more then the normal one, when you go back to normal mode, your PL is reduced by 1.5x-2x.)