I wrote almost my entire PhD thesis by hand, with a pencil. When I made mistakes I erased them. My handwritten notebooks contain close to the final version of each chapter (there were, of course, some further corrections after typesetting).

I don't like writing in pen. I like being able to erase stuff. Having scribbled out bits looks messy and gets on my nerves.

Whatever implement you choose, I do concur with the author that writing by hand is good for you.

I don't write much these days, but I do fill pages full of notes, mostly diagrams and other pictures. I don't understand how some people with jobs similar to mine don't use paper at all.