Now I wonder how on-site editing would have changed the plot of Stephen King's The Shining.
Jack Torrance sets up his office space and typewriter in the Overlook Hotel, and Wendy Torrance says "Jack, hon, you know...I'd have time to, you know, if you'd like, look over pages once you're done for the day, kind of keep track of the progress you're making, watch how things develop, it'd be good practice for me and it could help you..."
And Jack, only just about to start and not having had to gripe to her that her coming into his writing space breaks his concentration so that hasn't become an issue, considers her offer and says "That...that is not a bad idea."
Point is, Wendy Torrance would've spotted and flagged that whole "ALL WORK AND NO PLAY MAKES JACK A DULL BOY" business by the second time he'd written that. The story never would have gotten to here!
MAYBE IT WOULD HAVE GONE TO HELL A DIFFERENT WAY, but not that way.
And that is why