Even though I do teach some rescue skills in the OW class, all that's covered in the actual rescue course is not. There just isn't time. Rescue is the first course I recommend after open water. The YMCA and now SEI only require ten dives after the initial cert to take it. Other agencies require more dives or an advanced class of some type.
I do disagree with this because of the way resorts and dive ops view an advanced card in some cases.
That card is used to grant access to sites and dives that the course likely did not prepare the diver for if it was one of the "experience this type of dive" courses.
A good rescue class will be as much, if not more, about preventing accidents as it will actually dealing with them. Most actual dive rescues normally do not require great buoyancy, trim, navigation skills, or paramedic level CPR/FA skills. Most rescue tows do not involve rescue breathing on the surface due to the fact that unless you really practice it regularly, like an instructor gets to do, you're going to screw it up and just delay getting to actual help.
The average "Rescue Diver" I normally run into hasn't practiced one skill from their class since they took it. That might have been years ago. Yet they still brag about being a "rescue diver." No, you have a card, but you are not a rescue diver.
The other sad fact is that in a number of accidents, it's not going to be a rescue. It'll be a recovery. One that may be carried out by other divers or by professional recovery teams. Rescue Diver is not what too many people who put it off think it is. It's not public safety diving, it's not bringing the dead back to life, and it's not usually going to involve helicopters lifting a victim on a stokes to get them on board.
It is more often going to be towing an out of shape guy to shore who got overtired, helping someone with a cramp, or dealing with an overheated or chilled diver. You might do CPR in very rare cases. You might administer O2. More than likely dive pros on scene, the boat crew, resort staff, or EMS will do most of the heavy lifting.
What you are most likely to do though as a recreational "rescue diver" is prevent an accident from happening. By noticing those things that could lead to an accident. Divers with things out of place. Divers out of sorts getting ready to go in the water who shouldn't. Gear issues that could lead to an accident. Errors in judgment that could lead to someone getting into a situation they are not ready for. A good rescue course will cover that in detail.
The in water stuff will challenge you and push your limits if the instructor is doing their job. They will also tell you when you should step back and let pro's handle the situation. They will throw scenarios at you that you've not been briefed on just to help you see how you react to the unexpected. IMO every diver should take a rescue class or even workshop on rescue skills if one is offered in your area. At least on the basics. Like hands only CPR being able to do something is better than having to look back and see that you didn't do anything.
A rescue class will give you the confidence and some skills that will allow you to try. Sometimes trying is enough to be able to sleep at night even when things turned out tragically.