The value of having an editor
Writers who want to sell their work would do well to bear in mind that when they submit their novels or short stories for book or magazine publication, or their screenplays for sale or even option to a production company, they're bringing their inspiration-infused, hard-earned sheaf of pages to a crowded marketplace. It's really competitive out there.
There are a few who have clout with acquisitions editors or producers who have promised to buy their work. Lucky them. For most writers, having it easy to sell, even with a good agent, is about as likely as being Grammy-nominated for an air guitar instrumental.
The literary playing field these days is more un-level than ever. Even factoring in writing talent and in-vogue, high-concept storytelling, actually selling one's work is an uphill battle that could discourage Sisyphus. Having a good editor is no guarantee of a fat check. However, it can improve a writer's odds of selling.
A well-chosen editor will help an author hone his or her work to become its best. Even such literary luminaries as Hemingway and Fitzgerald owed debts of gratitude to their editor, Maxwell Perkins.
It's a time-honored adage, never more true than with author and editor: Two heads are better than one.