it "liberates" my mind. I can't keep all the details in my brain. Example: designing a system. I can see the system in my mind but at some point I need to dump it to paper, so I can keep thinking about it. The paper, with the design, is discarded later on... the next time I need to continue working on that system, I start from scratch (although it's way easier than the first time). At some point I have the whole thing so memorized that I can start working on it without having to check the notes. I know it sounds counterintuitive, but "it works".
Also, my notes look terrible bad. I don't even care about my handwriting at that point; I only care about "move stuff from brain to paper".