What an excellent post!
I have to disagree with the idea that wasting film in a hurry can be analogous to the artist's sketchbook. A sketch is an exercise in learning to see. The artist forces himself to work through the shapes, perspective and lighting and so learns to see the subject. Be it 5 min or an hour, time is invested and a final product in pencil or charcoal is produced demonstrating the challenge faced whether successful or failed.
Not so with blowing through 36 exp in 15 min. Here, instead of learning to see, the photographer is learning how not to have to see because surely something good will come from the roll. It's sort of like using a sawed-off shotgun for target practice. Surely one pellet will hit the bullseye but what is learned? What challenge is truely faced?
I find that if I invest the same in making an exposure that I do in making a sketch I get a negative worthy of printing. So I would say that my good negatives (as apposed to MY crappy ones) are my sketchbook.
Thank you Mr Wilson.