From Apple's Enterprise webpage for iOS 8:
With iOS 8, you can wirelessly connect iPad, iPhone, or iPod touch to Apple TV without first connecting to the organization’s network. Which means you can present or share your work even if you’re offline or the organization has a complex network.
AirPlay with no network connection will make it easier to beam presentations (and games) wirelessly to an Apple TV when you can't connect to the Internet. Apple allowed Bluetooth-based setups for Apple TVs last year, and it's good to see them extending AirPlay's capabilities to make it more ubiquitous.