Weight Vs. Size shouldn't be much of an argue meant. Give me a 2x2 box that weighs 100 lbs and I won't be able to carry it far. Give me an inflated beach ball that's like 5x5 and I can carry it all day and anywhere I can fit it.
I'd rather have a larger lightweight bag that has potential to store a little more extra vice a small bag packed to the point of the seams breaking and then go "Oh Sh--" when there's something I find and can't pack.