The Syrian army and the National Defense Forces have liberated about 250 km2 from the ISIS terrorist group in the eastern countryside of the city of Aleppo since the start a military operation in the area 20 days ago.
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Syrian Army Liberated ~250 km2 From ISIS Terrorists in Eastern Countryside Of Aleppo City (Map)
I can see the political point of meeting the Turks as close to Al Bab as possible. It might even be useful to establish a land corridor to the Rojava Kurds. But the Syrian army would probably have been of greater use militarily fighting against ISIS elsewhere.
The point is they are running against time to get all the strategic cities to avoid the split of Syria, al-Raqqa is already lost ot the kurds, but it seems there is some agreement with them already.