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...I use them routinely. They help to move my fat feet just a smidge farther out from the crank, and in many cases are the difference between the toe strap rubbing on the crank as the pedal rotates, and not. I have also not used them for many years before I started using them, and nothing bad happened to me.

Not sure why a Campagnolo crank set would be abnormally stressed by them, but suspect it has something to do with the construction of it. The mating surface of washer with crank and the mating surface of pedal shaft with crank is not all that different in area. But Campagnolo as a company has been telling me weird stuff for years...like their hand matched bearings stories.