The laws of the game clearly delineate where the referees should position themselves. The additional assistant referees (the official name for the goal line refs) are supposed to be on the same side as the assistant refs (official name for the sideline refs) because the referee positions himself at the top corner of the box on the opposite side of the field from the assistant ref. as such, he often cannot see the portion of the penalty box closer to the assistant ref and when there are lots of players in the box, the assistant ref also cannot see since he is 20-30 yards away. By placing the additional assistant referee there, the referee can see the box from the front and left side (when looking towards the goal) and the additional assistant referee can see the back and right side.

Here's a link to the rules of the game, where the additional assistant referee positioning is shown, which may help illustrate my point.

The laws of the game clearly delineate where the referees should position themselves. The additional assistant referees (the official name for the goal line refs) are supposed to be on the same side as the assistant refs (official name for the sideline refs) because the referee positions himself at the top corner of the box on the opposite side of the field from the assistant ref. as such, he often cannot see the portion of the penalty box closer to the assistant ref and when there are lots of players in the box, the assistant ref also cannot see since he is 20-30 yards away. By placing the additional assistant referee there, the referee can see the box from the front and left side (when looking towards the goal) and the additional assistant referee can see the back and right side.

Here's a link to the rules of the game, where the additional assistant referee positioning is shown. This may help illustrate my point.

The laws of the game clearly delineate where the referees should position themselves. The additional assistant referees (the official name for the goal line refs) are supposed to be on the same side as the assistant refs (official name for the sideline refs) because the referee positions himself at the top corner of the box on the opposite side of the field from the assistant ref. as such, he often cannot see the portion of the penalty box closer to the assistant ref and when there are lots of players in the box, the assistant ref also cannot see since he is 20-30 yards away. By placing the additional assistant referee there, the referee can see the box from the front and left side (when looking towards the goal) and the additional assistant referee can see the back and right side.

Here's a link to the rules of the game. The additional assistant referee positioning is shown on page 83, which may help illustrate my point.

http://www.fifa.com/mm/document/footballdevelopment/refereeing/02/36/01/11/27_06_2014_new--lawsofthegameweben_neutral.pdf

The laws of the game clearly delineate where the referees should position themselves. The additional assistant referees (the official name for the goal line refs) are supposed to be on the same side as the assistant refs (official name for the sideline refs) because the referee positions himself at the top corner of the box on the opposite side of the field from the assistant ref. as such, he often cannot see the portion of the penalty box closer to the assistant ref and when there are lots of players in the box, the assistant ref also cannot see since he is 20-30 yards away. By placing the additional assistant referee there, the referee can see the box from the front and left side (when looking towards the goal) and the additional assistant referee can see the back and right side.

Here's a link to the rules of the game, where the additional assistant referee positioning is shown, which may help illustrate my point.