So why is “never edit while you write” bad advice? There are two reasons:
1 The first is that writers often look for problems that aren’t there. The idea that “first drafts are shit” makes them think that they must make radical edits to every piece they write. Surely there are a multitude of darlings that need murdering in there!While under editing work is certainly a problem, it is also a problem to over edit it. You do not want to take your beautiful weirdo monster and defang it, clean it, and trim its fur until it looks like every other brown rodent in the park.
2 The second, and more common, issue is that the puke-up-a-draft-then-polish-polish-polish method can leave you with an unfixable draft.