Combo edge = best of both worlds.  Plain edge when you want it, serrated edge when you need it.  Serrated edge will slice through rope, seatbelt, packstrap fast if you need to, i.e. you swamp your canoe and are entangled in something and likely to drown.  Won't leave a nice clean cut, but will get work done in a hurry.  Also tends to stay sharper longer.