I would like to point you to this article, which explains why ink is so important in this course. Ink is also an hard requirement if you would like to receive official critique. Besides this however, and being the lessons free, you can engage them as you wish.

I still strongly advise you to try ink even though you are not interested in joining the Patreon. At first we all probably understand the argument only on a rational level, but as months go by and piles of paper full of warm-up exercises reach the recycle bin, one starts to feel the conscious control over the paper that this course teaches. It's also a lot more gratifying.