A flash, also known as a speedlight or strobe, is a device that emits a burst of light to illuminate a scene for photography. While the Sony a7IV camera has a built-in flash, external flashes offer more power and versatility, allowing photographers to control the direction, quality, and intensity of light.
External flashes are particularly beneficial in low-light conditions, such as indoor events, night photography, or when shooting backlit subjects. They can also be used to fill in shadows, create catchlights in the eyes of subjects, or add dramatic effects to a scene.