Caveman Charlie, I can tell you from painful personal experience that if the wipers are left on the glass, and if the glass is above freezing, and wet snow falls on the wiper blades, you can get some very thick ice binding the wiper to the glass. It takes a lot more than a bump to free the wiper blade.
Maybe because it is so much colder in Minnesota, that does not happen? It surely does in the Sierra Nevada of California. I see folks pull their wipers away from the glass whenever snow is in the forecast and have learned my lesson.
Apparently, there are wiper manufacturers that recommend this procedure, at least according to this article:
Lift those blades, they sayBut let me be the first to say that I am NOT an expert -- I am a warm weather flatlander who sometimes travels to high altitude. So if this is all bad advice, I am wide open to a counter-argument!!