Beethoven ... left behind an enormous number of sketchbooks, yet he said he never actually looked at them when he composed. Asked why he kept them, he is reported to have replied, "If I don't write it down immediately, I forget it right away. If I put it into a sketchbook, I never forget it and I never have to look it up again.
Fontanelle says similar things about Leibniz who, he says, took notes of everything he read and then added his own thoughts at the same time. Afterwards, he put it aside and "never looked at it again. But his incomparable memory forgot nothing that he wrote, as it usually happens [with others]. It was as if through writing he eternally engraved them in his head."
I am sad to say that this is not my experience. It might be that I remember things more easily after having written them down, but it does not seem to make much of a difference. I would be lost without my note-taking system.
1. And it does not make much difference (to me) whether I typed or hand-wrote the notes.