I do it as stress relief, for when I have no motivation. It took me about six month to get the main collection in, and now that that's done, when I feel the need to procrastinate now, I either to a re-organizing of the shelves, or I pull out some of the books-in-family-areas that I haven't got to yet. (There's still two whole rooms of this house I've barely started on, plus the bookhelf in the attic that follows the entire ridgeline of the house. But I got all of *my* books in.)