Correct Oz. It all depends in conditions. On hot humid mornings in Mexico we turned it on after start up. Gets rid of a foggy windshield quickly. Our SOP says we should turn it on through 10,000 feet. Different from Beech but they are bloody expensive to replace and you want them to work when you need them. And thats in Icing Conditions above 10,000 what ever comes first.
Had them on the Twotter Ive been flying aswell. Bloody waste, but hey they are Canadian Machines.