http://www.itkf.org/about_tk.asp about pulling your punches back, one use is in case you can't win the opponent in that just one blow, would you want your arms sticking there for the opponent to grab hold of it? and practicing drawing your punches/kicks back is also meant to promote control. you should be able to control your movement/attacks so the damage you do to the opponent would be in control. so if in a real fight you can't control your punches to hit your opponent in full contact, you have failed the training. if you cannot pull your kicks back in time when he's trying to grab it, you have failed your training also.