The Blast Furnace is used to turn Iron Ingots into Steel Ingots, which are essential in the RailCraft mod. It takes approximately 16 seconds to make a Steel Ingot, meaning timers must be set to four seconds for charcoal, 8 if using Coal Coke, and 16 secs. per Iron Ingot.
Coal (128 EMC) to Charcoal (32 EMC) yields four times as much Charcoal as Coal , but the Blast Furnace requires only twice as much Charcoal as Coal Coke . This way you'll need only half as much Coal to create the same amount of Steel , compared to using Coal Coke created in a Coke Oven. It's also much faster. The loss is that you won't gain the Creosote Oil that's produced when turning the Coal into Coal Coke unless you turn wood into charcoal in a Coke Oven.