Why would anyone want to do this?
I can think of several reasons. Initially, it'll be edge cases. Police officers on duty: it'd be great to record everything they see, as evidence. Folks with early stage neurodegenerative conditions like Alzheimers: with voice tagging and some sophisticated searching, it's a memory prosthesis.
Add optical character recognition on the fly for any text you look at, speech-to-text for anything you say, and it's all indexed and searchable. "What was the title of the book I looked at and wanted to remember last Thursday at 3pm?"
Think of it as google for real life.
We may even end up being required to do this, by our employers or insurers — in many towns in the UK, it is impossible for shops to get insurance, a condition of doing business, without demonstrating that they have CCTV cameras in place. Having such a lifelog would certainly make things easier for teachers and social workers at risk of being maliciously accused by a student or client.
(There are also a whole bunch of very nasty drawbacks to this technology — I'll talk about some of them later, but right now I'd just like to note that it would fundamentally change our understanding of privacy, redefine the boundary between memory and public record, and be subject to new and excitingly unpleasant forms of abuse — but I suspect it's inevitable, and rather than asking whether this technology is avoidable, I think we need to be thinking about how we're going to live with it.)