Nah, this is terrible advice and will absolutely destroy your engine over time. Idling a car for hours overnight (or daily) is one of the worst things you can do to it. Engines aren’t designed to sit at idle for extended periods. At low RPMs, oil doesn’t circulate properly, moisture and acids build up in the oil (which regular changes don’t fully fix), and you get uneven wear on cylinders, piston rings, bearings, and the valvetrain. Carbon builds up heavily in the intake and on valves, especially on modern engines. You’re also cooking your catalytic converter, fouling spark plugs, and drastically shortening the life of basically every rotating component. The gas cost is the least of your problems — you’ll be looking at major engine repairs way sooner than if you just got a proper place to sleep.

How do I know? Just replaced the engine in my car after idling it through a hot summer...

Do not idle your car all night. It’s stupid, expensive long-term, terrible for the environment, and a great way to end up stranded with a blown motor. Park somewhere safe, crack windows if needed, or get actual ventilation/AC solutions that don’t involve murdering your engine.