By that I mean you pick out common problems in your writing that show up over and over. Things like word re-use, character tics and all sorts of other problems. Once you see those tendencies you’ll automatically begin to compensate, and future drafts will be better while still being written at high speed. You’ll learn story structure, something that those who endlessly tinker with the same three chapters will never experience. Completing projects teaches characterization, plotting, pacing and a