It makes sense to clear the roof of the car, only idiots wouldn't consider clearing it, probably the same idiots who think its clever to drive in adverse weather conditions without headlights. Consider this, yo have 6 to 8" of snow on your roof and all of a suddne it slides off, have you no consideration for the following drivers. Aaargh, two of my pet hates, and while I'm about it, drivers who stop at roundabouts when the road is clear, middle lane owners club drivers on motorways.....I could go on, but I won't!