Part of being a writer is the act of writing, letting the words flow out onto the page. It’s a joyful thing when the words are coming fast and quick and wonderful. The sort of thing Mihaly Csikszentmihalyi calls optimal experience, a state where you are completely absorbed in what you're doing, in effortless control of the activity, unselfconscious about it, and at the peak of ability.
Another equally important part -- and one whose mastery can actually help you attain that state -- is the act of rewriting, taking the results of that flow and turning them into a wonderful writing.
If you know that you can do this, it helps with the act of writing, because you’re not worrying about whether what you’re writing is good or not. You know that what matters is producing the words, because you can trust yourself to make them better.
If you have a lump of words, you can always turn them into something, even if it takes resorting to outrageous techniques like a cut-up in the mode of William S. Burroughs. you have a blank page, your options are considerably more limited.
This class isn’t about creativity. But you will find that once you learn to trust your editing skills, worrying about the writing’s quality will not impede the flow -- at least as much, given that we are all a bit insecure. Think of trapeze artists - if you can trust the safety net that editing will provide you, you will be able to take the risks necessary to learn how to execute amazing aerial maneuvers in your writing.