How does having elements of the supernatural lend to a storyline? For example, in Macbeth, witches, a floating dagger, & a ghost (Act 3 scene 4) are part of the play.
Having elements of the supernatural lends to the storyline by adding dramatic suspense and tension to the play. For instance, in Act 3,Scene 4 of Macbeth, the scene where the ghost of Banquo appears seated on Macbeth's chair at the royal table and later reappears twice instills fear, tension and suspense in the audience owing to the fact that Banquo is already dead.
Elements of the supernatural also lend to the storyline by dealing with parts of the plot that cannot be explained by nature or science. Supernatural elements assume such uncertainties originate from beyond or other worldly forces. In Act 3 scene 4, Macbeth plans to visit the witches (Weird Sisters), hoping to learn more about the future amd who may be plotting against him. One has no way of knowing this in the realistic world and supernatural elements fill this void. The return of Banquo in the form of a ghost after he is murdered by Macbeth is enabled by supernatural elements.