The Lightning headphones will be capable of receiving lossless stereo 48 kHz digital audio output from Apple devices and sending mono 48 kHz digital audio input. The input means that the headphones will also support a microphone for audio input following Apples upcoming update. Manufacturers will be able to take advantage of Apple Headphone Remote controls like Volume Up/Down/etc, as well as other buttons for launching specific apps such as iTunes Radio or initiating playback controls on iOS. In addition, the headphones can be made to work specifically with a companion iOS app and launch a specific app when connected to an iOS device.
There are a few benefits of using the Lightning cable to send audio. Apple says the headphones will be able to draw power from an Apple device (even if the device is asleep), which for some products could eliminate cost associated with an internal battery. It could also work the other way around by providing power to an Apple device from an internal battery or external power source. That enables you to listen to music and also use a passthrough setup so you could charge the device simultaneously, much like you can with an audio dock that uses a Lightning connector. The headphones will also be capable of receiving firmware updates.