I was taught the side-slip during my PPL, but not the turning side-slip. The first time I saw a turning side-slip was with an instructor in the States, in a Super Cub. He demonstrated one first - in the circuit, downwind, abeam the numbers, cut power and full flaps, full right rudder, and almost-full left aileron as necessary to turn onto final. It felt like we were falling out of the sky!
Next time round, it was my turn, and I was far more gentle with the controls than the instructor. "No, not like that, like this", and the instructor pushed in full right rudder for me, and held it there, until I had the courage to use the necessary amount of aileron!
After a couple of goes, there was a twin a couple of miles out on the instrument approach. I expected ATC to have us extend downwind behind the twin. The instructor got on the radio to report "Super Cub 41E downwind, request short approach" "Super Cub 41E, short approach approved, cleared to land, number 1." What????? But, sure enough, with the aid of my new-found technique, we were on the ground and clear of the runway well before the other traffic was over the threshold.
It turns out that ATC at that airfield are very familiar with the technique, and quite often offer it to the club's taildraggers (but, as far as I can tell, only to the tail-draggers, and only to those tail-draggers operated by the that club!) Over the two months or so that I was flying out of the airport, there were about 3 or 4 occassions where ATC asked me "are you able to do a short approach?" Of course I was! I love the technique! It's just a pity that most of the noise-abatement circuits around SE England are so huge that I can't practice it more often now I'm back home.
Of course, as with all new techniques, don't try it without an instructor who's familiar with the technique, or, if you have to, at sufficient height to recover if it goes wrong, and I make no guarantees about it working on other types.
FFF
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PS - CFI & WWW - I'm sure this thread would be of interest to the Private Flying forum - any way we can copy it over there? Or should I just post a link to it?