As you might imagine, I am of two minds about the concept of "shitty first drafts." The idea, from the writer Anne Lamott, is that "All good writers write them. This is how they end up with good second drafts and terrific third drafts." The advantage of this approach is that it frees the writer from having to worry about the quality of the first draft. Even a good writer's first draft will be shitty, according to this logic, and so the difference is that the good writer writes something, even if it is shitty, and then revises it until it is good and then excellent. The bad writer presumably either writes nothing in the first place, or does not know how to revise. For the writer terrified of putting words down on paper, the notion of a shitty first draft is wonderfully freeing. This approach works for many people.
So what's the problem? At some point the writer needs to learn to write, not just revise. The first drafts will not be perfect, but they will not be shitty either. Revision will still be necessary, but much less. The experienced writer will avoid certain kinds of mistakes on the first draft. After all, if you can't write, you won't be able to revise either, because re-writing is still a form of writing. A good writer needs to know the feeling of composing a good sentence, once in a while, on the first try. I'd much rather have a model that emphasizes the development of the writer's competence.
If I find I have written a really shitty draft, what I do is discard it and start again from scratch with the same ideas but different words. Looking at my own crappy sentences is far from inspiring. Those crappy sentences don't suggest better ones to my imagination. In fact, there is a danger in revising sentences that were never destined to be great in the first place. If a sentence really isn't working, the problem is not a cosmetic one that can be fixed by revision. Erase it completely and write what you really meant to say.
Maybe I'm being too literal-minded about this. I would say the idea of a "shitty first draft" is, indeed, a stupid motivational trick, but it is not my stupid motivational trick. For the same reason, I hate the idea of a "rough draft.".