Sooo, what are we talking about? I guess a cool down is only needed if the engine is really hot like after track use or such.
Here in Utah we have some situations with stop/go traffic in 104F wheather, not good and the engine will be superhot. So on my way home I drive the last mile or so with med rpm and little load, does wonders for cooling down.
And yes, once I parked the car in the garage after a "hot run" w/o cooling down and guess what, blue smoke on start up the next day.
Later,
Andy