I'm a re-reader, so if I enjoy a book enough to re-read it, I'll purchase it, but ... I also use the library heavily, especially if I'm exploring a new-to-me author or genre, or going through an author binge (i.e. - the summer I decided to read most of Jennifer Weiner's back catalogue or when I read The Sandman in 2020) or whatever personal reading challenge I set for myself, like read more mysteries or try a contemporary romance, etc.

If I find I'm re-reading a book over the course of a checkout or renewing so I can re-read it, I'll add it to my wish list, either to purchase myself or receive as a gift.

So, for me, re-readability is a massive factor for purchase vs library checkout.