I'm currently flying in Canada and they have a different perspective to the use of carb ht in the circuit.
In cold temperatures, Carb ht is left on until full power is applied again(in a go-around or touch and go) then carb ht is set to cold. The engine will give a better response. It is also easier on the engine, I believe it's the same reason we wait for the engines to warm up before run-up or takeoff. In -50 deg canadian winters applying full pwr to a cold engine in not a good thing.
Safe Flying
Capt. M