iOS 8 uses peer-to-peer technology to stream video to Apple TV, as described by Apple on a page highlighting enterprise features.
Today, AirPlay requires both devices connect to the same WiFi network before they can communicate.
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With iOS 8, the network is cut out completely and the iOS device directly talks to the Apple TV with a peer-to-peer connection. AirDrop uses the same peer-to-peer technology, for convenience reasons.
The peer-to-peer feature could come in handy in enterprise contexts, such as when doing a presentation in a meeting, as well as elsewhere. For instance, players could setup a multiplayer iPhone game without ever needing to connect to the network, avoiding the hassle of entering WiFi passwords and such.