Coleridge, in revising, cut everything after "quiet moon." We discussed the revision and why he had made it (settling on a resonance created with the reiteration of the "secret ministry" that begins the poem), but agreed that the original final lines were lovely (for many reasons). At this, the professor said: yes, they are. But it is often the case that one must cut one's best lines.
His words reminded me of advice I had received (and since forgotten) in my MFA program: if you find yourself attached to a line -- remarking to yourself on how much you like it, keeping it in, draft after draft, even as other things change -- then it is probably a line you should cut.
Now, I'm sure there are exceptions to this rule, but in general, I've found it to be a pretty good one. And since remembering it, I've gone back over a few drafts of works in progress and made myself stop at every line that I really like and challenge myself: am I keeping it because I like it or because it is what the story/essay needs at this moment. Generally, I'm keeping it because I like it, not because it is "right." (This is, for me, particularly true of metaphors. I come up with some comparison in my mind that just works and I don't want to change it, even when other readers point out that it doesn't work for anyone else.)
I hope that others find this writing tip useful. If nothing else, it is yet another way to dive into a draft that you're almost done with a pay some close attention to language.