This was primarily the reason I started taking notes - I really had no plans to use them as references. However, three factors have changed my outlook on this:

This was primarily the reason I started taking notes - I really had no plans to use them as references. However, three factors have changed my outlook on this: 1) full-text indexed search, 2) cloud storage, and 3) low barrier to entry (I have found an organizational style that makes it easy for me to start writing at a moment's notice, without worrying about how to store/organize until later). Full-text indexing is a huge deal, because I will often remember a certain combination of words or a particular term used in reference to some concept. Cloud storage ensures that I am almost never without my notes. Add in the fact that if you make it easy enough for yourself to start writing, you will naturally end up with a lot of content about concepts you find difficult, and you'll skip the stuff you know well. The end result is a fully-searchable set of textbooks written specifically for your brain that you can always refer back to. Sometimes, even if I'm not looking for a particular note, I'll crawl through a few old notes on any random subject in my notebooks and it will give me a new perspective on a problem I'm trying to solve, or remind me of something I wanted to try/research but didn't get around to.