But keep in mind, just because it can hold more volume, doesn't mean the weight is irrelevant.

As a former handler I can't stress this kinda stuff enough. A small box full of nails weighs far more than a large box with cotton balls. People don't seem to get that. I had so many boxes break, or have the handles break because people over pack them. The other thing to know is that cardboard will get ruined if it gets wet. You might say why would that matter. Often times on narrow body aircrafts, the bags sit in open top carts, which are subject to the elements. Sometimes for a while. Cardboard box in the rain...not good.