I never open the windows. Always open the back door because it has a security door as well which is always locked. Too scarey to open them as I've been broken into twice at other locations and the feeling that someone has gone thru your private stuff is not conducive to a good night's sleep. Also all the neighbours leave their dogs outside and the barking is annoying.
I have the bedroom windows open during the day or when we go away, to let in the fresh air. I close them in the evening, incase I hear any traffic noise during the night. The bathroom, kitchen & laundry windows usually stay open during the night. Our house is high up, on the site of an old sand stone quarry, & 1 doesn't notice really the stairs from the roadway.