Police in Ontario recently stopped and charged a driver for having snow covered car windows. The driver got a $110 fine.
Ontario law requires that drivers have a clear view on all sides of the car. If your windows are not clear, you can easily miss pedestrians approaching from the side, or cars that are in an adjacent lane. Intersections are even more dangerous as your view of approaching traffic is impaired.
Leaving snow on your hood and roof of the car will also cause serious issues for cars behind you when the snow or ice blows off of your car into the line of sight of those drivers behind you. Ice strikes against cars in the winter are a source of car damage and accidents as well.
Please slow down in the snow, and be sure to clear your whole car including the roof and the headlights and tail lights.