Tyrone, thank you for your question.  I hope it didn't take you three months to get it just right.  In my case, what I'm writing back to you right now has gone through a treatment, an outline, a second outline, another treatment, another treatment of the previous outline, an outline of the treatment, four drafts of that outline without the treatment, then 7 first drafts, 6 second drafts, a draft of the first 7 drafts, and, finally, a polish... a polish of the polish, a polish of the polish of the polish, and, finally, the final polish.  (I think "Final Draft" should rename itself and forever from this day forward be known as "Final Polish."  On second thought, I think, instead, I'll start my own screenwriting software business and call it that.)  And, even after all that, I'm still not satisfied with what I've written you.  I know, somewhere deep in my screenwriter's heart, there's something I could be doing right now as these words come "cursoring" into being that there's something much more extraordinary I could be spewing forth, something so earth shattering that anybody reading this would pause with whatever they are doing and think to him- or herself:  "This is earth shattering."  But, alas (I like using words like "alas."  They make me feel like I'm some erudite ((ergo, the use of the word "erudite."  Not to mention "ergo."  The sign of a good writer is that he makes you spend your precious time finding your dictionary and looking up his pompous words.)) writer, who is extremely versed in literature and decided to not go on to receive his PHD because he just didn't want to carry around any more extra letters.), if I wait for that to happen, I'd never write one... single... WORD.

Polishing can be a very delicate act of kindness to your script.  Normally, it does crave your final touches.  Preferably, you've been making bold sweeps across the pages, letting your story and characters and emotions and motivations (I say "yours" because every script comes from you and is, therefore, yours) speak in an inimitably unique fashion that only you can provide.  You may have even done some "sweeping" and "tidying up" as you went along, being a born die-hard editor, unable to stop yourself from being your own watchdog as you made your merry way (especially if you're doing a story about Robin Hood) across the pages.  (I don't advise too much editing when first discovering your story, but, hey, everybody does it differently.  What would the world be like if nobody over-edited his or her stories?  It would be a very... over-edited storied... world, that's... what it would be.  I think, even though, I have named myself, "Script Advisor" I'll quit advising while I'm ahead.)

What I have found with polishing is that you want to do it with a precision, yet a precision that is both graceful and subtle.  I'm not talking about the violently-worded aspect of cutting.  The thrashing (I mean "cutting") of your script to fit the format, to fit the pace, to fit the storyline, to fit the premise, to fit the characters, to fit the dialogue, to make sure that it's not over 120 pages so it won't wind up as goat food at the producer's farm (where he gets away from it all so he doesn't have to read more-than-120-paged scripts and can feed his goats with them)... all that should have already been done before you move into your final stage of the writing your script ("Final Stage"!  Maybe that's a better name for my screenwriting software company.)  Now it's time for what has been dubbed "the polish." (Trumpet fanfare as the chariots round the last bend of the track and head for the finish line.  Where the lions await.  Very hungry.)  The polish can be an exhilarating activity not only because it means you're nearing that finish line (sans the lions.  Wait, I may have spoken too soon about those lions.  Check your finish line.  Any sign of twenty-year-old  studio execs just putting down their comic books?), but because it can be looked at as a separate art unto itself, an art that you want to master.  I call it "the touch."  (Actually, I just this moment, or this recent moment, called it "the touch.")  That's what you need.  The Touch.  (Capitalizing always gives an aura of importance even though it's only important in the eyes of the "capitalizer.")  

It's not easy to put THE TOUCH (capitalizing all the words is a way to "shout" it at the reader, which is usually not appreciated in CHAT ROOMS or even in COLUMNS -- unless you can get away with it because you're a recognized columnist who likes to SHOUT HIS WORDS) into WORDS (sorry) words.  How shall I describe The Touch? The Touch.  Since I named it, I should be the one to describe it.  This is not an easy task.  I guess you might say that you're fine-tuning, looking for the very best way to get across what you've already gotten across, but may be able to do it in an even more sublime, economic, and/or descriptive way.  It's a game of subtleties now (not "sub titles."  Unless you're writing a foreign film.  But, in that case, it wouldn't be foreign to you.  Unless it was and, in that case, I advise you do a lot more polishing.)

Regarding, your specific question, Tyrone, about when to stop polishing.  To answer that, let's consider that famous tale of "Aladdin's Lamp."  (Or, as the modern, rewritten version is entitled, "Al's Flashlight.")  If Aladdin hadn't polished the lamp he found, what would have happened?  Two words:  No genie.  So, in a weak correlation to the story, you have to polish to bring out your genie (or "genius."  Same Latin root.  And I'm not talking about trees in Rome.).  But, staying with our classic tale, if Al had polished the lamp too many times, over-polished, so to speak, what would have happened?  That's a good question and quite a conundrum.  Would the genie have appeared each time he did so?  And, if he did, would he have granted Al a new wish each time.  Or three more each time?  Or, after Al had polished his flashlight for the 49th time to the point that it had lost its original luster and unique quality (substitute here "your screenplay" for "the lamp"), would the genie have appeared for the last time and told Al to cut out the polishing or he'd polish him!?

Nobody really knows.  (Probably, nobody really cares.  But that's beside the point.)  If you, Tyrone, did want to explore the concept in terms of you writing a different version of "Aladdin's Lamp" in order to satisfy yourself on a visceral as well as an intellectual level, you could do it.  Heck, you could use the idea as a premise for a full screenplay.  A screenplay that could turn out to make everybody pause and say, "This is earth shattering."  And, as I've said to many a screenwriter when I've had the privilege of guiding his or her career, you're on your way.

Just don't forget the polish.  

(And not the kind you'll need to shine the shoes you will wear while accepting your Oscar for Best Earth Shattering Screenplay.)

DcH