What are examples of circumstances where rear curtain sync would be preferable to front curtain sync flash?
Second curtain sync is used when you want to get natural motion where light trails lead to an image as opposed to leading away from it. Normally a flash will go off at the start of a shutter (which is normally longer than the time the flash is active.) This results in a heavily exposed image followed by a trail of light. Second curtain reverses this by making the flash go off at the end so you get a trail of light leading to the more heavily exposed moment of time.