Why would I change either?
I mean, I’m a hoopy frood, So I know where my towel is, and it’s full of all kinds of nutrients due to the competing microbes that compose its flora. You don’t just waste that kind of ecosystem by changing towels every decade.
And sheets? What about the memories? Every stain is a mark of something wonderful that happened. Except the ones that are marks of something horrific that happened. Or the ones that are just spilled beverages. But, you know, that’s still plenty of good memories you want washed down the drain, you animal you.
Best be careful when changing sheets anyway. It’d be a shame if your mattress wasn’t properly killed before being shipped from Sqornshellous Zeta and it went on a flollop rampage after being exposed to too much sunlight.