A few years ago, I had a manager who made me take notes on what I was doing all day.
More than ten years later, I'm still at it. More from habit than design, I kept notes on who bought what, when, and additional things that might be useful.
My notes, that turned into a work journal, won't tell you anything that you couldn't find out elsewhere, but it's mine. Safe on Google Docs, and a few other places, pulling up relevant data is as easy as a Google search.
Yesterday, my new boss wanted to know about our in-house training. I emailed him thirty pages for him to plow through.
It's good to be able to produce documents...