You almost always remember more of what you have consciously written down by hand than by typing. You can write as little or as much as you see fit; the point is that the conscious involvement of "whole body and mind" in the act of writing enforces mental discipline, helps find inter-disciplinary patterns and in general, is an aid to thinking.
Here is an article on the brain areas involved in writing; Psychologically speaking: your Brain on Writing - https://uwaterloo.ca/writing-and-communication-centre/blog/p...
Finally, if you look at any of the great Scientists, almost all of them wrote prodigiously viz. Letters/Papers/Books/etc. I am quite convinced that this was one important factor in the development of their greatness.
My personal role model for writing is of course Edsger Dijkstra :-)