It can create confusion when working a motor vehicle accident on a 2 lane road, and all  the emergency vehicles, while parked on shoulder, have their brights on. Makes it hard to figure out where the correct path is, seeing the person in charge of stopping / directing traffic through the scenes. I was Chief in a department , had rule no more headlights left on at road scene than necessary. . Worked many incidents on Interstate-95 , solid traffic. Had one person on scene whose only job was watch oncoming traffic for errant drivers, and give alarm if needed for us to run from side of road. happened several times,hit patrol car.