What's Importance of a “Ghost Light”?

So the logical reasoning for a light to be on in the theater at night is for any person that is in the theater working late or something. The light from the so called "ghost light" allows them to see where they are going due to stages having so many hidden places, bumps, and holes. For others it could also be for comforting, for the play Macbeth is said to be cursed. Having the actors avoid saying the name and referring to it as "The Scottish Play", and even avoid quoting lines before performances in particularly the witches incantations. How do they perform then if they can't say the words? This all just sounds like superstitions to me.