At one point I was considering building something similar for myself. Basic idea was something like: Take one screenshot every second, caption the image somehow and keep both things around forever. Add in some adapters that can extract more information (if the browser was active last minute, gather all URLs from that minute and categorize, and so on with different things) and put everything into one location.

Purpose for doing this would be to get a database I can search/query when I kind of know what I'm looking for, but I cannot remember exactly what it was. Being able to query "show me all websites I've never visited before, but visited first time in week 35" would help me a lot to find those easier.

Also just having a recorded log of everything I'm doing would be helpful to see where I'm spending my time the most.