Complex sentence: Threshing floors would usually be in places likely to catch the wind-so that the wind would assist the separation of wheat from chaff, and hence it is plausible for the threshing floor to have been located on a high hill.
Split into simpler sentences: Threshing floors would usually be in places likely to catch the wind so that the wind would assist the separation of wheat from chaff. Hence, it is quite plausible for the threshing floor to have been located on a high hill.