Ars Technica caught this little tidbit from the iOS 8 release on Apple TV (emphasis mine):
And AirPlay now works with other iDevices, even if they’re not on the same Wi-Fi network—now, devices can form an ad-hoc wireless network and stream that way. We recommend using the Apple TV’s built-in security features to keep strange iPhones from finding and streaming to your Apple TV without your consent.
I think this is the most underrated feature that iOS 8 brings to the table. It brings AirPlay back to its roots: a true screen projection technology. This enables content from mobile phones streamed over LTE or 3G to be projected directly to your television without requiring the device to have internet connection. This is huge considering that broadband can be problematic at times.