"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.

...

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."

--Charles Stross, http://www.antipope.org/charlie/blog-static/2007/05/shaping_the_future.html