User blog comment:Jupie/duo supprt/@comment-184.175.18.10-20120619083956/@comment-5002283-20120619084753

So tl;dr

the enemy jungler will get more farm due to having 2 jungles and can give buffs to the other lanes and still have those for himself too.

He also can apply pressure to the lanes, where you cannot.

And there are tops who can hold 2 enemies off.