Well its not exactly hard to clear fresh snow off the average car,
Not only then "insecure load" issue but the visibility issue if you brake hard and it slides forward onscuring your windscreen or it flying off onto the car behind you and the excess weight affecting your cars stability when cornering....
I'm glad, i keep seeing cars with mountains of snow on their roofs, and it's really annoying! It either blows off like powder when they're doing 60/70 on A roads, or all falls off onto the road when they brake, making it slippier for other cars.
"a post on Greater Manchester Police’s twitter page, said: “GMP doesn't have a policy to penalise drivers who leave snow on cars, but asks you ensure your roof and windscreen are clear.”