Ever had a question that you really wanted to ask someone?
To our librarian friends: Is it true that books that haven't been checked out in a certain number of years will be destroyed?
I used to work at a library. In my system, there was a binder that went through all of the different sections of books, like "970-990" (Dewey Decimal) to "Paperback Science Fiction." For each section, it would tell you the weeding guidelines. The guidelines were a combination of last checkout time and age of the book, and, occasionally, edition/version. The age of the book mattered because some subject areas change more rapidly, and older books would be out of date in terms of the information they conveyed, regardless of how often they'd go out. Older computer manuals and health guides, for instance. Computers and health had the shortest lifespan of all the books I can think of.
So, for instance, for fiction, age of the book didn't matter at all. All that mattered was whether the book was going out. Now, if you had, say, three copies of the same fiction title, and two had gone out regularly but one hadn't gone out for four years, and your weeding guideline said to weed all books in that section that hadn't gone out in two years, then you'd need to weed one. However, it might turn out that one of the copies that had gone out regularly was ratty and torn, and the copy that hadn't gone out for years was pristine. So you could weed the oldest of the three and keep the nicest. However, if you only had copy of a book that needed to be weeded, and it was in great shape, then you still had to toss out a great book. Often the books of the least interest to customers were the nicest, newest-looking books--because they stayed so nice because nobody ever checked them out!
If you were weeding the travel guides, you might have an age guideline of 10 years, which means you'd weed anything with a copyright more than 10 years ago, a checkout date limit of 3 years, which means you'd weed anything that hadn't gone out in three years, and you might also weed out old versions if replaced by new ones. Fodor's 2010 Bermuda would be replaced by Fodor's 2015 Bermuda and you'd get rid of the 2010 version.
If condition was really bad on a book that was still going out, you could try to replace it with a better copy that was going out less, or you could try to order a replacement. I'm not sure how often the replacements actually got approved, though, as it was generally something you requested through the system and not a quick process.
Sections that tended to be bursting at the seams with books would get weeded more frequently out of desperation, because shelvers couldn't fit all the books in that section. Sections that didn't get as many new books and didn't increase much in size, those sections would tend not to get weeded as often. Paperback romances tended to have to be weeded *constantly* and I was sometimes told to override the weeding guidelines and weed even more aggressively, because there simply wasn't room (that was one of my sections). Foreign language, however, could often skip weeding for a long time, because fewer new books came into those sections, and they were used regularly, which always results in culling books overtime because of loss, damage, etc.
In my system, though, books were sent to be sold at a large system-wide booksale held every 3 months. It usually brought in in the range of $10k for the library system every sale, so it was a huge benefit to the system. There were a few books that we were not allowed to send down for the sale (mostly those outdated computer and health manuals) because people would not notice the age of the book, buy it, and then complain about the information being outdated. Those went straight to the recycler's. But in general, it was great.