The purpose for including the affair was to have character development in the story. Abigail was willing to do anything, including the attempt to try and kill Goody Proctor in order to obtain John. This also made the foundation of Abigail, Goody Proctor, and John and how they were all significant in story development. If the writer had left of the detail of the affair, we wouldn't know why Abigail was trying to get rid of Elizabeth unless we made blind assumptions.
