With a revolver there's absolutely no advantage since your assailant's reaction to the *click* will most likely be to pull the trigger again. So leaving that first chamber empty only knocks down your round count in a weapon that is already relatively short on ammo.
With the semi-autos condition three does make them safer. But keep in mind that if you NEED that gun, you may not have two free hands. And under certain circumstances racking the slide to chamber a round may be difficult, if not impossible. At the very least, it is time consuming.
Keep your weapon concealed, and your awareness up.
"And I'm tellin' you son, well it ain't no fun, staring straight down a .44"