The great carb heat debate!!!
Well when you apply the common sense approach from the constructive comments here, plus do some research into accidents in the circuit area that were most likely because of carby ice you view this differently.
Dixons Cider has a good point, in the right conditions with low or nil power set, ice can be quick.
I hold carby heat until over the fence, if i am busy with the landing i.e. crosswinds etc, forget the carby heat, if you land OK, if you decide to go around the plane will still perform better than that of a static ground roll even with the heat on. try it one day you will see the performance is not that bad, sure it is less, but not that much.
When you think about reducing power for decent, crosswind or where ever, pull the heat then pull the power, and leave it until you are sure you can complete the landing, then put it in. If its too busy, complete the landing and don't worry. If you need to go around the little lost will hardly be a problem. At least this gives better performance than the ice bucket you might have otherwise.
J