Best-selling author Kristen Lamb recently wrote an article entitled, "Editing--Are You Butchering Your Own Creativity?" She emphasizes that no editing should be done on a novel until its rough draft is finished.
We've all done it. Turning off my self-editor was a challenge I fought to destroy, and destroy it I did (as my alpha readers can unfortunately attest to). It's amazing how many more words per sitting you can get down when you're not analyzing them. Kristen explains,
"Editing too early can kill a novel. Yes, editing can be devastating to shorter works, but doesn’t have quite the killing power it possesses when introduced into longer works. In a novel that can span anywhere from 60-120,000 words (depending on genre), editing can be catastrophic if done at the wrong phase.
"If you are writing a novel, you need to leave any kind of edit for once you have finished the entire first draft. Breathe. Get a paper bag. You will be okay."
Her article is especially useful for anyone struggling with NaNoWriMo (almost the half way point, guys!), so I highly recommend checking it out.