Yes before driving and while allowing your car to warm up you should remove the snow off the car as much as possible.
Snow on your cars roof, trunk etc can fly off and land onto someone's windshield and then cause a car accident because they would not be able to see.
I actually saw that happen one time when I was behind a car and the car in front of that car had snow on the trunk and roof and the wind blew the snow off and it landed onto the cars windshield that was in front of me.
The cars driver then couldn't see and drove off the side of the road into the ditch.
The driver was okay but you should always clean snow off your car and make sure all ice is removed from the windshield and back windows as well as driver side and passenger side windows.