Using a gas grill is pretty easy. First you open the valve on the propane tank, then you open the burner valves. When you’re done, you turn the burners off and close the tank valve. This is the proper way to do it and absolutely the safest. You really shouldn’t leave the tank valve open. But let’s say you do. Exactly what does that mean.
What if the hose connection to the tank leaked or the other end of that hose at the burners leaked or the burner valve leaks or malfunctions?
What if a squirrel that happens to be smoking a joint while holding a candle for light chomps down on the gas hose? It would absolutely be a dangerous situation, mostly for the squirrel.
What if the propane tank valve fails to close? Tiny spiders are known for settling in inside these valves and jamming them up. There’s nothing you can do except to disconnect the tank and run over to the other end of the yard with it to stay as far away from the house as possible before it explodes. There’s gas spewing out into the air as you’re trying to steer clear of those citronella torches you’re now sorry you lit about an hour ago.
All of these leaks and malfunctions happening would be like Uncle Leo lighting his cigar outside in front of the sewer drain that Cousin Eddy emptied his shitter into a few hours before. It would not be good and too much to think about so it’s best to make sure you shut the tank valve.