My take is that if the pedal has a full round face that butts against the crank arm then a washer is of questionable benefit. Some pedals have their wrench flats continue all along the pedal spindle and thus contact the crank arm. Ther two flats on that interface can act like a cutter and establish a stress riser right at the crank's weak point, the pedal hole. I felt that the recent growth of pedal washers is as much about liability reduction as it's a arm material protection (when the arms are carbon, much less so with AL arms). Andy