ive heard because it decompresses the compressor when you turn if off before you turn the car off. and if your going to get back into your car 5 minutes later you dont want the compressor fully loaded.
My mum always turns everything off, I pre much just jump out my car.. I have a cool feature for my headlights tho, If I turn my headlights while the ignition is on and turn the key off or w/e.. when I open the door the lights while turn off till I go to start my car again. - Yeah I start my car with my headlights on.. even Highbeam sometimes.. Its a slower start then normal but idc
The AC compressor would cause Load making it harder to start
I wasnt sure what caused it, but I do think after time you could blow your Engine fuse.. Maybe
Im not sure if the ECU cuts the A/C compressor off at startup.I know it shuts it off once certain revs are reached,or if a certain load is put on the engine,but not sure about startup though.I might have to check that out.I always make sure its off before I start the car anyway.Same with the headlights.
EDIT: Just went out and checked it out.The ECU cuts the compressor off anyway at startup.The compressor comes on a couple of seconds after the engine is running,so there ya go,starting the engine with the A/C on wont matter or hurt anything.