Every time you take a picture, regardless of the lighting conditions. Use when the subject is in shadow or is "backlit" (when light is behind the subject). In low light, hold the camera steady or use a tripod.
Red Eye
In Red Eye flash, you can reduce red eye by using a preflash or by using automatic red eye reduction. To make the camera:
Preflash, turn the Red Eye Preflash on. (The first flash shrinks the eye pupil to reduce the chance of red eye.)
Flash once and automatically remove red eye, turn off the Red Eye Preflash.