Sometimes, you will need to take the flashgun off the camera but have them both fire at the same time. You could even have two or more flashguns that you need to go off simultaneously. Or you could just need the freedom to move around your subject or studio without any wires from the camera.
If any of the above is true, then you need to use a wireless flash transmitter and remote control.
Buy with confidence with these household photographic brands; Cactus, Canon, Hahnel, Olympus and Sony