Back in my youth (way "back in the day") I would have believed it. That's also when I replaced spark plugs/wires/distributor cap every 10K miles, changed the oil every 3K miles, and checked/adjusted my timing monthly.
In this day and age of technology I would be skeptical to do anything to upset the balance of mechanical, electrical, and electronic harmony if the truck is running well.
With 100K mile spark plugs, Top Tier gas, and quality full synthetic oil, I don't plan to put anything through the fluid systems to clean them like the old days.
Just my .02