This question came over me when I tried to fill my ship with some raw materials.
In fact ram materials take much mor tons than m³ but nearly every ship has more free m³ than tons. I can think of a need for it as long as the ship has hangar bays or docking bays but it also applys to every small freighter.
What I want to ask: is there something I can do with my spare m³? Are there some equipment, I can add to my ship? Maybe some sort of better (and stronger) engines to raise the weight limit while reduzing the m³ limit (because the extra engines take up space)?