Controlling the border region of Northern Iraq and Syria. Its strategic in many ways including the Oil. For the small number of troops it gives the Kurds and others time to breathe and with ISIS in Mosul recently wiped out some buffer in the region. Basra in extreme southern Iraq is on fire at the moment and this Syria/Iraq region could become another powder keg. No use in letting the Iranians kick it off.
Isn't that "fire" mostly Iraqis who want to kick the Iranians and pro-Iranian Iraqi leaders out? So the idea would actually be to let that powder keg go off, but block the Iranians and their Russki allies from putting down the insurrection?
I would guess that Iraqi Shia's who want the Iranian influence out are not going to like ISIS or AQ either, but are these Shia's a halfway reliable ally (something like 1/2 of what we have with the Kurds)?
There are too many questions for me to be comfortable with this, yet, although unlike many on FR, I understand the necessity of containing Iran...