Privacy people have been wanting Facebook to provide a "Clear History" type button/option for some time. Now, Facebook is doing it!
If you live in Iceland, South Korea, or Spain.
And it's only for "Off Facebook Activity," which is where the tab is buried.
And it doesn't really "clear" your history, just sort of disconnects some of the data from some of the uses.
Supposedly it does make what data Facebook holds on you more visible to you ...
(Naked Security does have a nice overview of what you can do to make your Facebook account more secure and private ...)