Purging Books

We're going to have a major purge on the books, which are taking up a lot of space, especially given that 80% of our reading these days is ebooks.

So I'm drawing up a checklist of reasons to keep books, with the idea being that a book that checks none of the boxes will go. Here's what I've got so far -- anyone got any other reasons for keeping books?

• flickgc or I will probably want to (re-)read it some time
  
• flickgc or I might want to (re-)read it some time, and it would be hard to repurchase/get an electronic version
  
• The book is rare or valuable
  
• The book is an attractive or interesting object in its own right
  
• The book has sentimental value, or has a story attached to it
  
• flickgc or I might want to lend it to someone else
  
• It's a reference book
  
• It's currently wedged under a piece of furniture to stop it wobbling

(According to the catalogue, we currently have 4,229 books. And I reckon the space each book occupies costs around £20 at current London property prices.)

ETA: The library is online here.