Milling & Handleability
The main operating costs, other than coal costs, are related to the milling and distribution of the coal to the blast furnace.  LV coals, compared to HV coals, are generally softer and thus requiring less energy to grind, but they require a higher energy to dry the coal down to a moisture level required to eliminate the risk of handling problems. 
Moisture in the pulverised coals can lead to handling problems in the PF bins and transport system.  Clays in the coal may worsen the handling problems associated with moisture.