Manuals instruct writers to work in stages—brainstorming, outlining, writing, and revising—each involving different intellectual operations best kept separate because they elicit mutually interfering mental sets. Notably, the reviser's criticalness defeats the writer' flow, causing writer's block; but the manuals overlook another origin of writer's block in the opposite attitude, which seeks formless flow.
Writing's iterative stages don't exclude the attitudes each subordinates; a writer attends to form more when revising than writing, but attention to form isn't absent from the writing stage nor should the writer try to totally remove the fabled inner critic when writing a first draft. That effort may be as common a cause of writer's block as the overcritical attitude: banning rather than muffling the sense of form takes the fun out of writing. The inner critic uncurbed makes writing too difficult; the inner critic excessively suppressed makes writing too painful. These affective signals are the writer's guidelines. Following the affective guidelines makes for writing with the greatest formal excellence compatible with keeping pace with thought.
Intentionally writing badly, even in the first draft, is unpleasant, and it's also impractical. Sloppy first drafts are inefficient because they unnecessarily complicate revision, but much more importantly, they're self-undermining. Working far below their formal capabilities when composing first drafts, writers not only waste a writing-practice opportunity but blunt their skill and acquire bad writing habits if they suspend all concern with their output's form.