When I stayed in hotels, as I did fairly often for a while when I was working in another city for several days each week, I occasionally wondered why the toilet paper would be folded into a little triangle each day.
Now I see that there’s a Wikipedia article about the practice. (Executive summary: to let the guest know that the bathroom has been cleaned since the last guest has used the room.)
Huh. Makes sense now that it’s been explained to me.
(I suppose I could wonder why they do it even if I’m staying in the room for several days, but it’s probably easiest to just do it in every room, whether a new guest is coming in or not.)