I think it is important if you try some of the drawings by Preston Blair, that you avoid copying directly from the illustration. Even if the result isn’t as stunning as the original, I think you learn most by using your drawing based on the original and try to make a new version that gives a better impression.
The idea is to learn how volumes behave when in motion, and also how to construct a strong pose. For that, a notebook with preprinted baselines for writing is ideal. You can’t be precious about your art, because it is unusable for publication. This means it is about the process, the technical aspect of drawing, just the thing you want in a notebook.
Let the precious artwork be for sketchbooks, which seem to be used more for exposition than for exploratory sketches, rough drawings rather than sketches that show something about how the artist struggled with the subject.
I guess most people don’t want any awareness of that struggle, but rather see a finished work, or something that is on its way to become a finished work, that was created without effort. It strengthens the romantic view most have of artists, that of one who conjures up an image out of nowhere.
That is all.