Having two belts means that the furnace array can be longer, accommodating more input. Using splitters and underground belts allows it to be more compact.
Finally completed the second set of campaign levels. That one level where you have to just produce a bunch of weapons and destroy the biters was kinda annoying.
I'm glad they weren't particularly hostile for the next level where you have to build an airplane. The lack of pollution probably helped; only four boilers were producing any pollution at all thanks to all of the electric furnaces provided.
