I learned to fly in the 1970s on a Continental powered taildragger. I was taught then to leave carb heat on from downwind right through to touchdown. Later, converting to Lycoming powered PA28s they told me to apply carb heat briefly on downwind and then to go to cold for the rest of the circuit and landing. In the light of all the above posts, this advise would have seemed to be very unwise!
I think previous posters are right that some advise seems to be handed down over the years without any re analysis from experience.
Nowadays, flying mainly Cessna 172, I frequently notice icing right after engine start and need carb heat during the first part of the initial warm up.