I think he is worried that the nut can come undone by a couple of threads before the cotter pin will touch the top of the nut and keep it from turning.
Flyboy, Is that correct?
Yeah, thats exactly what i was thinking. When i removed the old idler arm, that had happened. The center link was resting on the nut, with clearance between the center link and idler arm.
Between that clearance and the slop in the idler arm to frame joint, i could turn the passenger tire about an inch before the driver side tire would move!