Fill flash outside means to expose a subject where it lacks sunlight or other lights. The fill flash also eliminates shadows from pictures and can also be used for landscape photography. By using fill flash, it makes your portraits look more natural and even out colors of your subject. You can also dial down your flash for example having 30% flash and 70% natural light. To use fill flash the subject would have to be farther away from the actual flash to get a good photo.