Aside from that, it also hampers authors creatively. The difference between a great film and bad film can hinge on what happens in the editing room. It has to be the same for books.

Consider how hard it would be for a programmer to do their job if they could only write programs concatenatively (e.g. if the code you committed last week were a real commitment—set in stone and you were never able to refactor it or clean up the architecture, etc.)