That question is actually a very legitimate one.
As it was pointed out, if really REALLY cold, carb heat could put you right in the "icing zone". A rule I have seen and heard regarding Lycoming O- engines is no carb heat below -10°C.
I dont know much about the whirly birds but most fixed wing dont have a carb temp gage, so it's either full hot or full cold. And during part throttle operation (descent), where the icing is more likely, there is just no way to know how hot the hot air really is after a few minutes (colder exhaust).
And below -10°C, there should not be a lot moisture in the air anyway.
I stick to that rule and never had a problem so far... (and BTW, running at peak EGT during descent is also a recommended practice where I come from...)