The photo below was taken downtown Riverside California at around 10 at night. This image was exposed for 1.8 seconds while an off camera flash fired from camera right.
Had the camera been allowed to control the exposure, all you would see is the couple in the foreground and a sea of black behind them with no people in motion and the buildings would barely be visible.
Create the image you want in your mind, and then use your camera's controls to achieve the result you want. Don't always let the camera choose for you.
