I wash them whenever I've dirtied enough for a full load, and if I don't, I'll often throw the bathroom mats in there with them. Frankly though, still nowhere near often enough. If they pass the sniff and squint tests (smell and look fine), I'm usually OK using them again. And again.

There was already a towel wash pencilled in for this week or next, oddly enough, before this question showed up, or else it might have shamed me into considering it. Other laundry is first in the queue though.

As for throwing them out? Never had need in the 20+ years I've had my own towels, and some of those were hand-me-downs.

I remember one particularly large brown bath towel starting to fall apart at my parents' house long before I moved out, and I still kind of miss it, which is kind of funny.

Now, washcloths made of towelling material - I've ruined a fair few of those with careless wringing. PSA: Don't fold them diagonally before wringing them out.