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.
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.