Plays
In the professional world, this individual is prepared to jump in for one of the leading characters should anything go wrong.
Double points if you can tell me why, practically and based on the superstition.
It allows the first person in the next day to find the light switches safely, and allows the ghosts of the theatre some light to perform by so they don't feel left out and mess with your shows.
Okay now leave, spin around 3 times to the left, spit, curse, and knock and I'll let you back in.