If this box is enabled, and a reader enters this page as a frame, an automatic Javascript will move the reader to the frameset. This is useful when a reader enters your site from a search engine. 
By the way this script may conflict with some kind of Special Links, and may give the apparent behavior of blocking the "back" arrow of the browser (it does not block it, but 2 clicks are required to go back, due to this automatism that implies a redirection)