How much docs do you actually write when working solo?

I used to skip writing down anything because it was just me and i had everything in my head. But then i took a short break recently and completely forgot why i made certain decisions in the code. Spent hours trying to figure out my own stuff.

Now i just leave quick notes on things that aren't super obvious. Nothing fancy just a line or two so future me doesn't get stuck.

Where do you draw the line between useful notes and just wasting time on docs?