Now that I have Android 5.0 on my Nexus 7, I have just had the opportunity to see another feature in action. I was using my Bluetooth keyboard with the Nexus 7 and up popped the trusted devices feature. This keeps the Nexus 7 unlocked in case there is a “trusted” device connect to the Nexus 7. The trusted device in this case was the Bluetooth keyboard. This feature was mostly talked about with the advent of all the smart watches and you can see from the feature screenshot that it is primarily for that.
Works well and I look forward to Android 5.0 on my OnePlus so that I can really use something like this with a smart watch. I can use it with the Nexus 4, but the battery life on that phone is preposterous.