I try to backlight my clients whenever possible during the course of a wedding. The effect is to create a glow around their shoulders, arms and head. This creates a floating sensation as the subject is separated from the background with a gentle wall of white light.
When I can, ill bounce a light off a wall behind me to throw a little on their faces.
In this image I underexposed a 1/3 stop for the white dress. This helps maintain details in the dress.
Black and white editing always look classy with this effect. The dark jacket is contrasted with not only the white dress but also the glowing white background.
Canon 5d mk3
50 mm 1.2 L
F 4.5 1/500