Here is what you can expect to do with this new Xbox Companion app:
Using the Xbox Companion app you can learn more details about the movie, TV show, music or game that is playing on your console. You can also get friend activity (friends online, friends with beacons, friends who have recently played), achievements and related items. You’ll also be able to select a search result, and launch a movie, TV show, game or app on the connected console as well as play, pause, fw, rw the playing video or music on the connected Xbox,initiate media purchase and navigate your Xbox console with Windows Phone using the Xbox Companion.
I am looking forward to using my Windows Phone devices as a remote for the Xbox rather than having to find a charged up controller around the rec room. It is great to see Microsoft providing integration across devices and I imagine we will see even more of this in the future too.