This fixes one of my biggest annoyances with iOS7 Safari - that it 'steals' 50px or so of tappable space at the bottom of the screen. If you try to use it, it shows the bottom bar instead of allowing you to interact with the page.

That said, this is kind of not-good-at-all. An individual page shouldn't be able to control UI like this, IMO. A lot of the changes Apple made to Safari in iOS7 were bad ones, and they seem to have invented a new meta tag to get around admitting that they mis-stepped.