Why? Because, trust me, over-writing can suck the life blood from your work, leaving it in much need of a laxative.
Try to remember your reader is reading your story for the first time. Their eyes and minds will be fresh and eager rather than bleeding. Chances are they won't give a flying 'F' about the correct usage of the Oxford comma, or occasional lapse in the sequence of MRUs, not if your story flies, not if your characters rip free from the page and not if you have succeeded in transporting them into a world they never want to leave.
If you have done a half decent job on your story (getting the GMC up front and central helps), they will not be bored stiff to the point of applying leeches to their eyelids and throbbing temples. Chances are they will be too engrossed and therefore, forgiving of little tics and errors. (Best to avoid sloppy typos and poor spelling though, they'll skin you for that or worse, abandon your book.)
So, don't hate your manuscript. Recall the verve that rushed through your veins as you punched out the first draft, because that is what it means to write from the soul. That is what will give your book its unique personality. All over-writing ever achieves is frustration on your part as a writer, and a Mogadon-effect in the reader.
Hence my new mantra: It's not as bad as it looks...maybe? (bites knuckle)
Caveat: This mantra does not excuse crap writing!