I was hoping someone else would answer this, so I wouldn't have to give away my age.
Some of the muscle cars we had in the late 60's and early 70's had run on problems. Probably due to some combination of high compression, advanced timing, lean idle (for smog in 70's), cheap gas, and a hot motor (as we always ran em hard all the way to wherever we where going).
So when we pulled up at our destination; we just blipped the throttle & cut the ignition. This sent a rich gas mixture into the engine, which prevented the run on (i.e. dieseling). If you didn't do this, some of these cars would sit there and diesel for about 20 seconds (pretty embarrassing).
Some cars got around this by putting a solenoid on the throttle stop. When you cut the ignition, the solenoid would deactivate, allowing the throttle to close down all the way.
Hope this helps as I'm feeling old now...
