How much paperwork is really required for a solo entrepreneur?

As the only one who works on my product at this point in time, I've had a habit of neglecting all sorts of documentation for ages. I was familiar with my product well enough not to get lost in details and to know what was going on and why. But after a two-week break, I couldn't recall some of my own decisions regarding a particular aspect of development.

Now I make myself take a minute or two to leave comments to any decision I've made that wasn't obvious enough, so that I won't have to go through the commit history each time I return to it. It's already helped me save some of my time.

What's the border for you, fellow solo founders, between helpful documentation and a time-waster?