I wonder to what extent there is a wider issue here, of which sometimes incorrect use of carb heat is a symptom.
Older C150/C152/C172 aircraft, carb heat is a very good idea on approach. However, most PA28s it's specifically not required - the POHs are very clear on that point.
Similarly, sideslipping with full flap in any PA28 is a good way of losing excess height if you make your approach too high. Do that in a C172 and there's a reasonable risk of undemanded motion - which is precisely why it's recommended against in the POH (which again usually gets treated as a prohibition very often) .
Yet, I've flown with instructors who insist upon carb heat on finals in a warrior, and other instructors say I shouldn't sideslip the same type if I'm high on finals.
In my opinion, there are too many instructors who in the search for standardisation look to teach single "one size fits all" techniques that will map to any type. Again, in my opinion, this is just plain wrong - the right way to operate any particular aeroplane is individual to that aeroplane; by default as given in the POH, and differently only with careful and deliberate thought.
G