It doesn't have to be. I don't think there are sufficient empirical studies to suggest writing by hand is better in some dimensions than typing.

I prefer it myself for several reasons. First, it forces me to filter the present jumble of ideas in my head into a linear progression on the page. Second, it helps me resist the temptation to edit myself before I have finished. I tend to be more mindful and focused when writing long-form.

Writing digitally, which I often do, comes with the temptation to edit and succumb to distraction before I've finished a thought. It allows me to explore many branches quickly... but quantity is often not what I'm after.

I think what you consider sufficient has more to do with your personal process and what you hope to achieve with your writing, if that makes sense.

Personally, I've found computer writing is perfectly fine for note taking; but, once I actually want to compose something that I've really thought through, I'll turn to handwriting for complete sentences.

I think the internet generally makes way too much out of which tool you use. Use whatever works for you and what allows you to do it consistently.

This -- like a LOT OF THINGS IN THIS SPACE -- is one of those things where you just *have to experiment* to find out. Do not strongly take advice from anyone or anything, it's probably a lot like e.g. 'favorite text editor' wars.

There is definitely something about writing by hand that seems to have unique cognitive and memory benefits. But strictly only writing by hand is unnecessary and of course inefficient.