I think the amazing thing here isn't the fact that you can get a picture which pretty well matches your posture, but rather that they've been able to train an AI to determine were all your limbs are moving just from pictures in a room with previously unknown light settings.

Just imagine how useful this could be for analyzing surveilance footage. Instead of watching through hours or days of surveilance video, you could just let a program scan all videos for a human action which matches what you're looking for. This is just an example of the top of my head.

The app itself serves no purpose other than being cool and attracting attention. I did try Move Mirror. In my opinion it didn't work well enough to give me the impression that the people in the pictures were moving like me. It seemed more like a laggy sequence of random images, so I suspect that they've spent some time finding good examples for advertising. Super cool, nonetheless.