Fourth, we will restore our deterrence with Iran. Tehran will no longer be able to bleed us through its proxies in Iraq, and we will be much freer to hit Iran — should we ever need to — once we’re out. Moreover, Iran will by default inherit management of the mess in southern Iraq, which, in time, will be an enormous problem for Tehran.
This the fourth "advantage" of little Tommy Friedman's wonderful idea to have a withdrawal date from Iraq.