The main reason for linkage rockers to start rotating freely on the shaft is when the stroke of gas pedal is longer than the stroke of linkage mechanism. In such case the linkage mechanism would come to the end of its stroke while there will be still travel space for gas pedal. Pushing the pedal would put a lot of stress on the linkage mechanism that is already at its maximum stroke. It is important to synchronize gas pedal and the linkage, so that the full throttle is determined by gas pedal stroke, not the linkage stroke.
Saying that, I do not like those linkage rockers made of stamped steel. They look flimsy. I already ordered billet rockers and they should arrive next week.