search-engines-web guy dug up an article about a Massachusetts public library that has run out of space for new books. As a result, they've had to throw away weed deselect older books from the collection to make room for the new books coming in. They can't stop buying new books, even if they wanted to. In order to get state funding, they must spend 19% of their budget on new materials.
"Throwing away books is the worst thing a library can do," Robertson said.
"We try to pursue every option we can before we throw a book away," Bachtold added. "We're librarians."