I live in the Pacific Northwest, which means temperatures don't fluctuate too much into extremes.

I personally like having the window cracked at night in the winter. I like to have fresh air, even if it's cold. I feel sick if a room feels too stuffy.

Spring, summer, and fall the windows are definitely open at least at night if not during a larger part of the day. If it's ~15-25C outside, I'll usually have at least one window open. More likely two in the 20s. I just don't tolerate heat well, so I will close my windows during the heat of the day when it approaches 30s.

Otherwise they're only closed if outside is gross (smoke, people talking, hazy) or if I want total silence.