Lou and I have using cameras for a long time. Long before we have things like digital sensors, auto focus, before even camera phones. We used light meters to determine exposure and we didn;t see the images we captured for perhaps a week after the shoot. But when it comes down to it, all a camera does is record light. Nothing more, nothing less, film, digital, professional camera, phone or disposable, they all just record light.
That's really what the skill of a photographer is all about, seeing and controlling light. On a given shoot, we may be carrying anything from small speedlights powered by AA batteries, perhaps something more powerful, like my Lumedyne or Orlit battery powered strobes. When electricity is easy to reach, it's really nice not to have to worry about batteries running low and I often carry my Dynalite studio system with me to weddings and mitzvah receptions.
Now sometimes it's not possible to bring my own light and I have to rely on my eye and skill to see light that it already there. Todays digital cameras can work well with a lot less light then film cameras did years ago, so that helps. But there are still many reasons that require no additional light be used. Perhaps were climbing into dense foliage and no way to drag a light and stand there, or perhaps were at the beach and it's super windy. Perhaps were working in a busy retail location and it would be disruptive to the merchant that was kind enough to allow us to use their space. Regardless, it's up to the skill of the photographer to see light, then position and pose the subject to use what we have and create beautiful images. Here is a sample of images created using only the light that was there.