The value depends on a variety of factors.
In some cases, older information is just as relevant (art books for example). Additionally, older items can serve as a historical perspective or be used as a comparison to current conditions (histories, of course; or the state of the Internet in the late 1990s vs. today).
Occasionally out-of-date items are "weeded" from the collection. Weeding is the process of withdrawing unneeded and outdated materials and removing them from circulation.
