If I had a spare bedroom, and guests, I would leave the room to them anyway. No need to go there. If I needed to be there, I'd knock.
Bedrooms in houses of other people, none of my business to go there.
I like my privacy respected, and assume others want the same.
Though, people who tell me "for the love of god, do not enter" in my house..... That would get me on edge. They're in my house as guests. No way they can tell me what to do there.