I think we bought our house because of the built in bookcases in one room. We added them in another, and lots of other freestanding shelves are in the house as well.
In the next house, I'm designing a separate library, with growth space.
What's really bad is moving out of a place with numerous built-ins into someplace with very few. "Storehouse" has those DIYs and I practically lived there for weeks on end ... "just need one more".
Then 10 years later I unexpectedly had to give about 15-20 of them to the Salvation Army and move into a hellhole cave. Also gave away probably 40% of my books, but I have always kept them thinned pretty well (ho, ho, ho).
Not the cookbooks, however. Around 700, maybe a few more. Miss them like crazy - can't even get into the storage unit(s). Ha, cookbooks are the only ones that used bookstores will actually pay money for (not much, but you have to *pay them* to take the others) - and I said "are you nuts? Who would part with a cookbook?"
Nearly all my books are non-fiction and reference, so it's always hard to give them away, except to libraries where they'll continue to be read.