My dad worked on the lighting crew for theater at Bob Jones University back in the late 50's early 60's. He has told me stories working with the open rheostats-and how they would sometimes stick especially during rapid transitions-leaving the operator the object of the directors frustration.
I am amazed at how may people open panels, etc without paying attention to their surroundings-clearances/people in the area. Especially with live audio/lighting I would think others being around could be a major concern. Part of the arc flash standard is setting up barriers for when you are in a live panel. Maybe not as practical for a quick hookup, but having somebody in the area that may not be paying attention has always made me nervous.