It improves the payload fraction of total mass. That is generally better. But you might have to factor the expected total mass into the design. If you want to t

It improves the payload fraction of total mass. That is generally better. But you might have to factor the expected total mass into the design. If you want to transport the payload mass of a 747 in lead bars, the smallest plane that can fit the volume will certainly not work. But a plane designed for that lead load would be far more efficient than a 747 (or modern equivalent) that is flying almost empty by volume.