YSK that if you have an air conditioner you should turn it on before you need it.
YSK because the first hot spell is when most people discover their AC unit is broken.
Several years ago I waited to turn on my AC. This is how I found out about one of the busiest times for repairmen and had to sweat for two weeks. Now I do a test run a couple of weeks before it heats up. Same goes for the furnace at the end of Autumn.
It was probably running R-22 which you can still get but it isn't manufactured anymore. It's ozone depleting so all production and import of the stuff was completely banned in 2020 and it has been in the process of being slowly phased out since 2004. The only source for it is stuff recovered out of other systems or any existing stocks which are running out very quickly. That means it gets more expensive every year. Now a days most HVAC companies will just replace those systems rather than fixing them for that reason.
Most machinery lasts longer when you run it every month or so at least. For an AC unit there is lubricant in the refrigerant, so circulating the refrigerant once in a while keeps the seals in good condition. It would also keep the moving parts of things like fans from corroding and seizing up.
For vehicles, running the them occasionally circulates the fluids like oil and antifreeze. The oil keeps the moving parts of the engine coated and doesn't allow things like condensation to rust the internal parts.