Often, plays being staged require different methods for immersing the audience in the scene. Smoke machines may add an element of mystery or the macabre to a scene. They also may be employed to momentarily obscure other parts of the set or props from the audience's view.
One of the great benefits of a smoke machine is that it does not actually produce smoke. Such an element would not be good for either stage actors or the audience. Instead, the machine really creates fog or vapor that is harmless and does not have unwelcome side effects such as coughing.
Smoke machines are especially used in plays that contain supernatural elements to their storyline. Charles Dickens' "A Christmas Carol," with its array of ghosts and spirits, is one example. Stagings of Shakespeare's "MacBeth" also frequently employ smoke machines, perhaps to augment the eeriness of its three witches.