I have never had to do anything close to a rescue myself. I was once in a situation in which someone near me ran out of air (she had apparently put her BCD on a used tank and had not checked) and grabbed her buddy's octo, but that is an OW skill. I was also near a situation in which a diver successfully rescued his buddy in a cave in an apparent oxygen toxicity situation, but that is more advanced than rescue.
As for the rescue diving course, the key feature is the scenario in which an unconscious diver is found after a search, brought to the surface, given mouth-to-mouth resuscitation while the rescuer removes his or her gear and the victims gear, towed to the shore or a boat, removed from the water, and then given CPR and oxygen. I would really like it if someone would supply a case in which that full scenario has ever resulted in a survivor.
As for the rescue diving course, the key feature is the scenario in which an unconscious diver is found after a search, brought to the surface, given mouth-to-mouth resuscitation while the rescuer removes his or her gear and the victims gear, towed to the shore or a boat, removed from the water, and then given CPR and oxygen. I would really like it if someone would supply a case in which that full scenario has ever resulted in a survivor.