Khan Sheikhoun is right on the main road (M5) of the Syrian heartland. It is the frontline for the Regime to push further North.
The main target in Khan Sheikhoun would be the munitions production facilities, which are inside of manmade caves, quarried into the solid rock, a bit like Cheyenne Mountain. Russian partisans sheltered in underground caves while fighting Nazi occupation, and have prepared similar cave-like military facilities in many of their client states. They tunneled out caves in Afghanistan that a whole Armored Battalion could comfortably park and live inside, with multiple entrances, in case some were bombed shut. 500lb aerial bombs or barrel bombs would not worry folks inside those caves, but they are open to the air outside the entrances - the wind just blows in for ventilation. The Syrian Army used these facilities for a long time before the rebels captured them, so they knew well that conventional bombing would be ineffective.
