I was talking to my sister, whom I'll be visiting soon. I spent a week with her back in May. While chatting, she said, "Oh, I haven't put on clean sheets since you were last here - the bed has only been used once since then when A (granddaughter of a friend) had a nap when she was visiting." When I visited in May, DSis hadn't changed the sheets since my previous visit in February. I only have a little twintub which I have to stand over while it does its not-terribly-efficient stuff, but when anyone stays over, I strip the beds as soon as they've gone, even if I know they will be back the following week.
The weird thing is that in every other respect, DSis is a much more particular housekeeper than I am: eg every bathroom is cleaned daily, including mopping the floors, the main rooms are hoovered every day, the kitchen floor is mopped after every meal, etc. Washing isn't a problem for her as she has a super-duper state of the art Miele machine; and, for instance, it's not unknown for her or her DH to have a couple of changes of clothes in a day - everything gets washed after it's been worn once.
And WIBU to strip the bed "to help" at the end of my visit? (I always offer this and she always turns me down; it's only today I realised why!)