I'm a bit of a connoisseur in bed sheets. Well, I did wash and iron 22 sets -king, double, single- every week on a changeover!
So, the worst culprit when it's hot is suncream on the sheets. It's often greasy, sticks to the linen and even stains it a yucky orange colour.
Next is drinks. People take cups of tea, coffee, wine up to bed, and of course accidents do happen. When you're in a holiday home, you're more clumsy because you're not used to the furniture around you.
Also, make up, hair dye, nail varnish- you name it.
And that's without a description of bodily fluids!
It didn't really bother me if I saw bed linen out on the line mid-stay. The guests were either swapping beds, which was fine by me, or trying to wash out the problems as mentioned above.
When you're on holiday you should be able to do as you like, the property is yours for your stay.
If I were with friends and swapped beds though, even after only one night , I would certainly wash the linen before using it.