How is Iran benefiting?
Shia vs Sunni. Afghanistan could now invade, although they’re probably too self-centered to accomplish anything.
Iran benefits because now they do not have an American intelligence and military presence on their doorstep. And an airbase from which drone strikes and other hostile air actions are at close range.
#16. Remember the old Islamic/Arab adage, “The enemy of my enemy is my friend” even if only for a temporary common cause (as happened in both Afghanistan and Syria.