I’m using a speedlite as a fill flash for outdoor portraits on harshly lit days without a lot of cloud coverage. This will lighten shadows on your subject’s face but won’t affect the background exposure—it will fall off by then.
When photographing people by additional light or strobes closer to them or vice versa for more flattering light.
When clouds drift in front of the sun, shadows get less distinct. Add fog, and the shadows disappear. Clouds, overcast skies, and fog act as diffusion—something that scatters the light in many directions. On overcast or foggy days, the entire sky, in effect, becomes a single very broad light source—nature’s softbox.
Shooting on a day without much cloud coverage? Materials such as translucent plastic or white fabric can be used to diffuse a harsh light source. You can place a diffuser in front of an artiflcial light, such as a strobe. Or, if we’re in bright sun, I use a light tent or white scrim to soften the light falling on your subject.
Bouncing light acts as diffusion.