Most people think that the purpose of attic ventilation is to remove moisture from the attic. That may be true in the spring, but the rest of the Canadian year it does other things.
In the summer it generally reduces the temperature of the attic, reducing the need for or the cost of air conditioning.
In the winter, it's real function is not removing moisture (which is frozen solid if around at all), but it keeps the roof and its snow pack frozen. Continuous ventilation that flows under every inch of the roof deck will prevent spot melting and then ice dams or ice cycles from forming on the edge of the roof. That is why baffles are so important to keep insulation from touching the roof around the edges.