[iggldiggl]

Generally I'd agree with that and I never leave the engine running just to save myself the bother of scraping (and ideally I've remembered to cover the windscreen with a plane the night before so I only have to scrape the side windows), but I'd make one exception: Sometimes the weather conditions are such that the windscreen immediately starts icing/fogging over again, in which case you really need to leave the motor running at least two or three minutes for the heater to at least minimally start working, so you can actually see where you're going.