Program Mode is a Professional photographers Auto mode. Full auto on your DSLR is basically turning it into a point and shoot camera. With Program mode, you can still have that auto functionality, but you can still have some control over your camera. You can't directly change your aperture or your shutter speed, but you can disagree with what the camera calculated by turning the dial you turn to change the exposure compensation. That same meter will either change the exposure to either brighten or darken the photo. Forgive me Nikon users if I get this information wrong. You can still change most of the other settings in the camera, such as the ones below:
- Focus Mode
- Frame Mode
- White Balance
- And more...
(If you don't know how to change these settings, please refer to my guide to Manual Mode and your camera's manual)
So, if you you ever have a time where you need to get your camera out quickly to get the shot, and don't have time to change settings, then switch your camera to program mode. This mode allows you to still have some control over your camera while doing the main calculations for you. Beware, since you can still change a lot of settings, make sure you have all of your other settings are set correctly otherwise you may get some nasty effects.