@Julie143 I suppose this will depend on if you are on hand to re stock towels. While our space isn't shared, it is attached to our home.
For a standard 2 night stay, we leave 2 towels per person. If the stay is for longer, then 3 per person.... but no more than that! I don't like the idea of wet towels piling up.
When they arrive, I tell them to let me know if they would like more during their stay, and that I will collect the used towels from them and swap them for fresh ones.
We don't take bookings for longer than 7 days, but in all the time we've been hosting, I've only been asked once for fresh towels. We've had people stay for 3 or 4 days, that have only used 1 set of towels for their entire stay.