Pace, as I said, if you extend downwind you may well cause problems for everyone else in the pattern and this could, in many cases, have been resolved earlier by extending upwind. At a military training airfield, where things are perhaps more strictly controlled and circuits are required to be flown to a fairly tight pattern, you are likely to be deemed to have left the normal circuit by extending downwind and unless given permission by ATC to extend you may be required to cross to the dead side whilst maintaining circuit altitude and fit back into the pattern, before you enter the final leg of the circuit.
Having been trained by the RAF over forty years ago (and later trained others to fly) and having now had over two decades of civilian flying, I think the military method provides a safer option for everyone concerned.
