Right but lets say I design a ship, and I'm happy with its cosmetics and performance, and it has empty space (this describes a ship I just finished actually). It's got empty space that exists because of cosmetic design decisions I made. Probably not great decisions, but hear me out - are you saying I should add more components (+mass) to the empty spaces? I'll have to add thrust and power to compensate for anything I add.No, it is quite the opposite in fact. Because the surface area of your ship that contains the volume used by systems has a mass cost, having unused empty space inside your ship 'increases' the mass of your ship relative to the systems blocks it is using.
I guess that probably the answer to that question is: Yeah, why not? :p I could make the jump computer charge faster, or I could add more shields/rechargers, etc. I get your point I think - if there is empty space then there is room for optimization, therefore it is not as efficient as it could be.