That's right! Do it whenever suits you. It's a very useful challenge to push through, but ultimately details like texture are not what this course chooses to focus on. The core of this course is focused on developing our intuition of how forms relate to each other in space, and how to make those forms appear solid. Texture, along with other details, are less important than the structural integrity of what you're drawing, and while they can make a well structured piece really pop, no amount of detail will improve or hide a poor construction.

I think this is why Uncomfortable chose to include it as a single-page exercise in lesson 2 rather than mandating the full challenge - the details are secondary and much less important than the underlying construction of the forms. In the interest of keeping the course more narrowly focused, topics like adding detail (things like texture) are touched on only briefly, so that students don't lose focus or deviate from the goal of this course: constructing solid, consistent forms. I believe the ethos here is that wrapping a "bad" texture around a solid form will always look better than slapping a "good" texture over a poor construction.