Whether or not this app is really necessary, I leave up to you. What it does do is allow you to access your Xbox Live account on your iPad, and give you limited control over your Xbox 360’s functionality. With My Xbox Live, you can contact your Xbox Live friends, change your avatar, and view achievements. More useful is probably the ability to browse games while taking a look at news, videos, and tips about those games.
If you’re watching a movie on your Xbox 360, you can also use the app as a remote control. It’s also possible to pull up console history, but it’s not really clear why this would be more advantageous than just using an Xbox 360 controller to do the same job.
My Xbox Live seems a little gimmicky, but, being free, you might as well give it a try to see if you prefer it to using an Xbox 360 controller as your remote. You can get it now on the iTunes App Store.