A lot of the answer to your question depends on what plane you are talking about. Some planes turn better with ailerons only than others do. The big limit you'll see by not having a rudder is you can't handle nearly as much wind. When turning from upwind to downwind, the wind pushes your tail out of the turn, forcing you to roll nearly sideways and use the elevator to get through. That works, but it makes for such nicer turns (and far less stall prone) to be able to horse it around with the rudder.