More depth of field. Focus and shoot. Good with most closeups. Open the shutter and set off the flash. Flash can be anywhere as long as proper distance from subject is maintained.
Photographer can fire off flash.
Requires dark room. Dim light behind the camera can allow for movement. Headlight must be off. Flash Synchronized - uses flash attached to the camera via PC cord or slave unit fired by flash on the camera. Advantage is no need to turn off lights.