This is one of those things that is recommended because of a problem that "might" be caused by using SeaFoam.............

As the detergent does it's job, there will be some carbon flakes that will break loose and pass through the engine. Some of these, if large enough and shaped correctly, "could" become wedged in the plug electrode and cause the plug to either fire poorly, or possibly becume shorted out. There also exists the same scenario with the 02 sensor.......carbon becoming lodged on the probe and causing an incorrect reading. Like yourself, most prople won't benefit from the replacements unless carbon fouling becomes apparent.

Just a side note.........after you add SeaFoam or Marvel Mystery Oil (if you pour it in the intake), have another person blip the throttle while you hold a towel in front of the exhaust. You'll be amazed at the carbon fragments that come out.