Which effects does the setting of the opening scene have on the play Macbeth?

It establishes the mood of the play, as well as the location. The witches enter with a storm, signifying the unpredictability and violence that is to happen in the play. They also mention the "scottish moor", so this sets in stone that the play primarily takes place in Scitland. Besides these reasons, during the time Shakespeare wrote the play, witches were a big interest especially for King James, so it was a sort of treat to the King as well as an opening that would immediately grab attention. Therefore, this setting acts as a form of a narrative hook, as one of it's main purposes is to attract attention so that one will keep watching.