I was once the first person on the scene of a rolled vehicle in a canyon on a busy two lane road. It was so soon after, the tires were still spinning on the upside down car. Once I had determined the passengers were all unhurt, directing traffic turned out to be the most valuable and useful function I could perform. That and telling the drivers that everyone was OK and to keep moving. I'm quite sure that my using a light to direct traffic saved some people an hour in a totally unnecessary traffic jam. It allowed the EMTs and cops to get up the hill faster, too.
You just don't know what role circumstances may thrust you into, particularly in an emergency. :shrug: