It's a cool insight that I just learned, but if the two gears share a multiple, then the same teeth will engage with each other over and over leading to uneven wear pattern. If the gears are relatively prime (e.g. 6 and 17) then each tooth will touch each other tooth before repeating the cycle.
Try it out on a piece of paper and see for yourself (that's what I did).
Try it out on a piece of paper and see for yourself (that's what I did).