ATF has cleaning powers. I don't recommend this for anything fuel injected, as I don't know the actual effects on those systems, but my father is an old school mechanic. My chevelle sat for a few years, idled like **** after we finally got it started and then my father threw some ATF in the carb, probably like 2 cap fulls, ran like **** for like 15 minutes, smoke everywhere, he just kept revving it to keep it running until it cleared out and everything was running much better. He said it helps to clear the varnish that builds up on valves that makes them move sloppily while also cleaning the walls of the cylinders.
Now fast forward, I had an old 2 stroke weed wacker that seized up on me. Not so much that I couldn't get a revolution out of it, just very tight in the cylinder, I could barley pull it. I popped the spark plug out put a couple cap fulls of ATF in the hole and let it sit for a while, came back and pulled it a few times, it started to move freely. Put the plug back in, started it up, ran like **** for like 5-10 minutes and then it functioned like new.
I'm no scientist but if ATF is a myth that's one hell of a placebo effect.