Only then is editing added to the mix. It is not the orderly procedure taught in earlier days. It's very messy in fact. To my knowledge, there is no definitive research on the subject. Here's what I see though.
Students are less afraid to write.
Many are eager to do so. They are not so worried about mistakes that they seem paralyzed in front of pencil and paper. Their stories show more of their natural inventiveness. Writing becomes fun. Activities that are fun are engaged in more frequently, and frequency increases skill.