Bah! Manure fosters growth ... the explanations provided by these guys is the equivalent of toxic waste. Maybe they originated from New Jersey.

The way I see it, there may be a very small possibility that charged molecules, in particular carbon, may be attracted to oppositely charged terminals, and build up on the spark plugs, which could cause high resistance around much if the spark terminals, meaning that the spark would eventually come from only a single area, which would eventually erode from the sparkle always firing from the same point. Eventually it would wear down so far, it would cause misfires.

But if they said that, rather than the gobbledy gook they do, they might convince someone.

But that said ... the last time I looked (1 week ago) fuel injection cleaner does exactly that (cleans carbon buildup from the fuel injection nozzles & the spark plug, and it only costs $12 for two (6 monthly) treatments. It'd take 4.5 years before the ($50) device would pay for itself, assuming it worked.