Cover your camera’s flash to create softer light over faces in portraits, to make things easier later on in Photoshop
A sheet of white paper will help reduce the impact of the light across the person’s face and diffuse flash light.
They are helpful if there’s no available surface to bounce the light off, and also give a wider spread of light.
This saves having to create adjustment layers and masks in Photoshop to even out bright spots of light that can sometimes appear on the forehead and cheeks of people.