The best useful purpose for headmounted displays is lifelogging. A reasonably high definition stream with audio and video of everything you see during a waking day (call it 16 hours) is only about a hundred gigabytes.

There's no reason not to do it, at this point. Imagine if we could go back and look at the lifelogs of historical figures. In order to achieve that, you basically have to archive everyone, since you don't know in advance if an individual is going to be important later in life.

People complain about the panopticon, but I'm interested in the opposite.