I took to closing my office door almost as soon as I moved into the new office. It's not that I have any great need for privacy - if I did, it would be the wrong office anyway. The walls are paper-thin. I'm sure anyone on the other side of the wall can hear everything I'm doing, from talking to typing to thinking.
The reason why I close the door is simple: my office door is directly across the hall from the handicap washroom. I'm not a manager and even if I was, I like to think that I'm not the type to micro-manage to the level that I care how much time people spend peeing.
Even if I don't care how much time people spend peeing, I get to find out anyway. Remember how I said the walls were paper-thin? That extends to the washroom. I can hear everyone peeing. I can also hear everyone washing their hands. So good on you, folks! It's important that you spend as much time washing your hands as you do. I appreciate that, but I don't really want to hear it.
The other down-side to this door/office proximity problem is that I think it makes other people uncomfortable. Maybe they feel they have to chat. Maybe they're slightly embarrassed to be using the handicap washroom when the other washroom is the next door down. Maybe they wonder if I'm judging them. (I'm not judging, by the way. I have a shy bladder and can't pee if there's anyone within half a mile that might hear me. It's like nobody pees but me. Maybe I'm not alone and everyone else goes in there for a bit of privacy.)
So if you walk past my office and my door is closed, I'm not looking for privacy, I'm not mad, I'm not secretly constructing a robot to do my nefarious bidding - and I am nefarious. I just happen to think that it's easier on everyone if they don't feel like I'm monitoring their arrivals, departures, and off-loading of baggage like a judgey airport.
Trust me on this: my door is always open, even if it's not actually open. Just remember: I'm on the right, the washroom is on the left. If the room your in doesn't have a toilet, turn 180 degrees and it should be right there.
(I also think that pooping at work should be illegal, but that's for another time.)