Local governments and services such as toll booths have been using things like this for years. Ironically they have entered the consumer market via the Y2K issue. But obviously we can see they have a much broader reach in California for example. My insulation is blown in and goes right up to the roof line and there is not much room for air flow from the outside. If the insulation is so thick that it presses up under the roof sheathing, then no air will be able to enter the soffit vents below them.
Ventilation is important year round.
In the summer it keeps the attic cooler which makes the cost of air conditioning that much lower. The snow on your roof will have no impact on your heating bill specifically and can be dangerous to remove. You can do so safely with a roof rake which looks like a wide gardening hoe with about a thirty foot long handle. Removing the snow may, however, reduce your chance of getting ice dams which can cause damage inside the house. Most homes today even those two or three years old do not have enough insulation.