a cutter with a perfectly square chisel would take only one-pass per cut of a grain-thread, if you think of grain threads going vertically up a tree. or better said, each pass of a perfectly square cutter would take out x-number of grain threads, cutting each grain thread to full kerf width.
a cutter with a rounded chisel would take several passes (several cutters) on each grain thread, to fully cut back the grain thread and open up the kerf to full width. the first pass (first cutter to nibble on a grain thread) might cut that grain thread back to say a half-kerf's width, then depending on roundness, subsequent passes (cutters) would nibble off grain-threads sideways, until the kerf was fully opened up.
in small wood (with higher percentage of bark to cut thru), a square chisel might be 10% faster for the first hour or two, but if you're given only one chain and a file for a day, I'm not sure a half-chisel of full round might not cut more wood by the end of the day (e.g. be faster!) than a square chisel. so for limbing/firewood saws, there is definitely a place for the "softer" chains. which seems paradoxical, because a round cutters also take more passes thru the bark, so if it's the bark-scum that does the dulling, the round cutters should also get more dull in bark too -- so maybe the grain structure of bark is different than that of wood, such that the round cutter is more efficient in bark than a square cutter ...