I don't keep them closed all the time, if the weather is stable or anticipating a shot opportunity they are open (stalking, calling, etc). Only when required are they closed and then a scope full of snow or debris, fogged, etc is no better then a lens cover! Bonus is being attached to the scope when I come in from a day and need to wipe down my rifle I have no worry about solutions or oil contact the lens surface and degrading the coatings.