Fresh air breathes life into us. Cracking open the car window on a long drive. The occasional winter day warm enough to open the windows, even just for half an hour. Fresh air freshens.
In a building, fresh air is called ventilation. We have national building standards about it. Engineers make a living calculating it. Sometimes it's referred to as HVAC. We can think of it as fresh air.
How do we bring fresh air into our homes? Especially in the winter, when good health is harder to come by? Typically, a combination of open windows, and gaps in the floors, walls and ceilings of our houses. So our choices are fresh, cold air dribbling in through the building, or lots of fresh, cold air pouring in through the window.
Its like riding a tandem by yourself. The second seat is redundant because if you use it, you can't steer.