|Peshmerga Approach Frim Baaj and Tal Afar|
This will be a major blow to ISIS because Sinjar holds open their supply routes from Raqqa and other Syrian cities to Mosul. With Baiji and Tikrit now firmly under control of the Iraqi army and militias there is also no major roads leading from ISIS held Ramadi and Fallujah to Mosul.
Going forward ISIS is going to have to commit large forces out in the open to carry out an offensive large enough to take back territory to open these key routes otherwise they'll be limited to using less accessible desert routes to transfer supplies and fighters between their key cities.
This all ultimately boils down to the battles for Mosul and at some point Raqqa. Cutting key supply routes will make it very hard for ISIS leadership to glee these cities and even harder for them to send reinforcements when these battles take place.