I love that feeling that I get writing for closure, when I'm distilling and crystallizing things that I've learned about a topic. I use physical notebooks for that kind of writing, and writing the words out by hand once I've understood something just feels so nice and durable. And then I can page it out of my brain, knowing the notes are there if I need them again.

(By contrast, I'll usually have a temporary digital file with notes in flux while I'm learning something. But the notebooks are where I write things "on-the-record.")