One may think that the job of an AR is the ball in and out and offside. But ARs play a vital role especially when the referee is caught behind and ends up significant far from play. In the video below, the referee is extremely far from a possible foul incident. In this situation, the AR is the only one that can make a credible decision.
It is important to note that during this counterattack, there was no imminent offside decision for the AR to make. There was not going to be any ball in-or-out decision, either. This means that the AR’s focus must be 100% on the play itself. The AR is now the “referee” who happens to be on the touchline.
AR’s focus and involvement is critical in making a correct decision.