Thank you Eastmeg2 and Davidh10 for your input in this discussion. David, what you have said is, in my opinion, correct. All reciprecating engines that I'm aware of, will benefit from the technique you have described when descending from altitude with the throttle closed (for whatever reason and/or weather conditions) because it helps to control/reduce the engine's rate of cooling. And then there's the added benefit that if the engine does "quit" during the descent, you'll know about it earlier than you would have, had you not done this gentle "test".
The idea though, of increasing to full power and then back to cruise power every 2 - 3 minutes during cruise is not something I agree with. Please bear in mind that if your flight manual says to do it, then so be it... Do it. Beat your engine up... But if your flight manual doesn't say to do it... Don't.
At the risk of having the aeronautical design engineers amongst us cut me a new ring gear, let me try to explain in a way normal people can understand, why we shouldn't "pump" the throttle during cruise. Every time we go up to full power and back to cruise, we're whipping the engine. The internal temps increase and then decrease, even though we don't see it on the guage. There's lots of different/dissimilar types of metal in our engine. They expand and contract at different rates, and they remember, because all metal has a memory.
Keep the sunny side up,
Wayne