> What possible use could there be for doing this?

Early detection of disease, as well as every kind of physical issue with the body you can imagine.

The incredulity of the question seems rooted in the medical culture of our current time. It's easy to imagine a science fiction future where scans happen not every 9 months, but daily, in your home, and the idea of not constantly checking your full body would be as strange as not brushing your teeth is to us...