Bad light produces bad photos. If your subject matter is a grand landscape, a huge building, a towering bridge or any other large item, the sun is your main light. If it’s obscured by ugly clouds, too contrasty or the wrong angle, not much can be done to improve the light except return on another day. But, if the subject is small enough to be lit with a flash, bad light can be augmented and even overpowered and made to look good. On small subjects, flash can be used to fill in shadows.