Guest room door whiles guests are out: open or closed?

I can offer no insight, really, other than different folks are comfortable with different things I guess.

Our situation is same as yours; rooms in our home. And like you, the vast majority of our guests leave their door closed pretty much at all times. Which I think is fairly normal behavior. Or at least that’s what I would probably do if I were a guest in someone else’s home.

I personally am more comfortable when guests keep their door closed while they are here. It affords me privacy as well as them. As for the ones that don’t, I guess they just have different boundaries.

If guests are out of the house, have left the door closed, and I’m confident they will be away for several hours, I will sometimes open the door to their room for a few hours for the sole purpose of letting the “inexpensive” heat or cooling from the heat pump warm or cool their room. Otherwise, if the door remains closed, the more expensive furnace heat or window A/C unit will kick on in just that room.