Well as the rear trailing arm goes up and down the rod end will pivot on the bolt but will also move in the other axis ( misalignment ). If the rod end is not locked (jam nut) in the female threaded tube welded to the plate, it is likley that the rod end will not only pivot on the ball of the feim, but will also move ( turn) in the threads, It is not a big problem becasue it can only turn so far, but it can over time wear your threads out. I was just being picky
