Books can be valuable even if you never read them again, in several ways. If you have kids, you never know what they might read, or just what attitudes they might pick up from the presence of books. If your books are in a public part of your house, guests may see them and either start a conversation or be impressed. If they are behind where the guests sit, you may see a book a guest will like and give it to them. Also, of course, there's the potential for bathroom reading, a page of an old favorite.

That said, when you're moving house, you should be more ruthless than usual with books.