I would guess this is one of those subjects where everyone knows the "correct" way of doing it, and will try to shout down any other methods
Personally, I was taught to apply carb heat as part of the downwind checks, and either remove it on short final, or else either on go-around or when clear of the runway (depending on instructor).
I don't fancy the idea of a quick check on downwind, then leaving it off for base and final - I have flown aircraft which, at the low power settings used on base/final, would certainly get carb icing in this short time without carb heat applied in normal UK weather.
On a related note, it is scary how easy it is to forget habits. Having learnt to fly in a PA28 with carb-heat, then moved to a PA18 with carb heat, and occassionally various other aircraft with carb heat, I now mainly fly two aircraft which don't have carb heat controls (one uses the supercharger to heat the inlet air, and the other is fuel injected). On the rare occassions when I find myself with a carb heat control, it is very easy to forget to use it
FFF
---------------