I did see a show a while back were a mechanic/engine builder was talking about rolling on the throttle from time to time on an older engine. I don't remember the model engine and it was a few years ago.
What he mentioned was that it was not good to run a a constant rpm for a long time. It was something on how the engine pumped oil and goose-ing the throttle from time to time increased the oil pressure to force it to the highest portion of the engine.
But, if you "slow down" you will eventually have to rev the throttle to get back up to speed. So, no matter what you do first (slow down or speed up) you will have to do the opposite at some piont.
Now, I am sure some sage advice will be coming as to whether this is true or not and what models it applied to......:s
I do not believe this applies to recent engines (fuel injected)