My friend has a 12 volt cooler in his storage bay outside. He uses it for cold drinks. It is fine to leave it running as long as you are plugged into shore power or driving down the road. If you are boondocking for any length of time, he generally will unplug it. It will drain the house batteries down if you leave it plugged in too long while there is nothing charging the batteries. They still use their normal fridge as they always have. I couldn't see someone using a small cooler in place of a normal fridge. It has no freezer to start with.