I have a heavy duty receptacle like this that I haven't used yet - for one reason ... too lazy to run heavy enough wire to it from the coach batteries so as to take good advantage of it's 20 amp maximum current rating.
These type of heavy duty but classical style 12V receptacles would be great for: 1) Mounting so as to be accessible from the outside of the RV for accepting up to 20 amps from, say, around 200-250 watts of portable solar panels, or 2) Mounting inside the RV with heavy enough wiring (~8AWG?) for plugging in portable 250-300 watt inverters that you don't want to wire in permanently and that you don't want to shut down and starting chirping from voltage sag on their inputs.
Our motorhome came with multiple interior 12V receptacles and one exterior 12V receptacle, but none of them are heavy duty enough. :(
