All things being equal (money, space, etc), would you rather own copies of the books you read? Or borrow them?
All through my life, I have always done both: Bought some, borrowed some. As much as I love books, I dare not think what my home might look like if I had bought and kept every book I ever read... In real life of course both space and money DO matter; and living in a small flat rather than a big house puts a limit to how many books I can have in my own home. And I do not really like permanent piles of books on the floor so I try to keep within shelf-space!
A key word to me is probably "easy access" rather than "ownership". Most of the books I buy and keep (especially in later years) are such that I find it likely that I may want to reread, look things up in and refer to, "at any time". With new books/ authors I often borrow first and then if I find them really good I might end up buying my own copy. Other reasons to buy rather than borrow may be that the library doesn't have it (for example if I want to read a certain book in English); or I want it NOW and there is already a long queue for it at the library; or I know I want to read it, but not just now, and when I do I can't be sure it will be available; or I suspect it may take me longer than the library loan time to read it.
But I love the fact that we have free public libraries which provide a wide choice of literature for anyone regardless of how much money they have. I'm sure there are lots of books I would never have read and lots of authors I'd never have discovered if I had had to buy every book to be able to read it.
Some of my Arthurian and other mythology books.