MSD Ignition Question

Okay, this is just a cruising car, no racing or anything like that. I'm not opposed to using a MSD box, I just wanted to know if there is a disadvantage to not using one, or would the masses say, "hey, you should use one because of this, this and that".
correct me if i'm wrong, but i think ignition boxes give you multiple sparks, completely burning the fuel, resulting in slightly better mileage?