I used to have a huuuge physical book collection, but meeting my minimalist wife and having to move around pushed me to donate most of them (I have pack rat tendencies so this was a big deal for me). I made a list of the books I donated for any future needs (to rebuy, to borrow, etc).

My setup is now this: -I have a list of books I want to buy/rebuy in physical format someday, ideally very nice hardbacks - books I can read and display really nicely. Most of these are series and I have ebook copies of them, so I can read them at any time. -I use the library for a lot, both physical and digital. Some books I borrow and then realize I want my own copy; I might buy the ebook version now, or I'll put it on a list to purchase some time.

Ebooks have really helped conserve space while also allowing me to "hoard" the books I want or need!