Old school guys want to do it the old school way. The truth is that way back when that was the standard it wasn't because it was better. It was because 4 channel radios cost more and servos were heavy and expensive so going the rudder only route was a lot cheaper on the newbie. If you're already set up with ailerons, you do have the option to just not use them assuming your plane is a traditional trainer style. But let your instructor show you his way to do it.