What Nick & John have said is the case. Many older camera and studio flashes may route anywhere from 20-250 volts through the shutter sync contacts. Not a problem with most older cameras, disaster for new digital and film boxes. The Safe Sync is the solution to that problem. I have one that I use inline with my old Photogenic AA01-A power pack to reduce any potential for arcing, pitting, or welding. Too many lenses and cameras that parts are no longer available for.
Here is a good resource for determining the sync voltages of various flash systems:
On the RZ due to the sync being in the lens, most of these should not be a great consideration, but the safesync is not a bad deal, again to reduce pitting and other problems.