i was always taught that anything up to 20deg
in a cess was o/k, otherwise tou can mask the rudder, as already said.having said that
i've slipped a 150 with 40deg of flap after an engine failure climbing out parallel to the field with too much height for a normal approach. made sure the speed was above normal, and those barn doors sorted the rest out on very short finals. mind you it was the wobbliest back-track you ever did see,due to legs of jelly!