Someone else on the boards told this story a while ago, so I'll try to paint the setting.
Two people wanted their picture taken in front of a BEAUTIFUL sunset. So, they asked one of our board members to take the shot. He asked if they had the flash set up correctly, and they responded that it will come on if it needs to.
Of course, when the camera is pointed directly towards a sunset, there will be enough light so that the the camera believes a flash will not be needed. Unfortunately, all that light is coming from behind the people.
Those two people ended up with a BEAUTIFUL sunset, and their two silhouettes in front of it. In this case, a little fill flash would have lit them up from the front as well as capturing the sunset behind them.
FlipsidE