As an old newspaper reporter, I can tell you firsthand how it interferes with the writing process when the editor stands over your shoulder. Yet, most of us do this to ourselves every time we try to write.
Writing and editing are two different functions. You will do a better job with less stress if you will separate them. When you write, write. Don’t worry about punctuation, editing, spelling, etc. You can clean that up later.
If you think you don’t have time to do that, let me tell you: you don’t have time to not do it. It actually takes less time to separate writing and editing.
Since we are concerned with helping you speak more effectively and avoid writing it out word for word in the first place (because you’ll then sound like you’re reading, even when you’re not), it’s even more important to find another way to prepare for your speech—and this is it.