Using up extra space
A good way to use up the pesky extra space on huge ships eg. Leviathans is to fill them with Point defense chassis missiles with all the extras of your latest missile. That way, kinda like what Thorax said in 'Hit and run', before your ships move in to fire on them with their real weapons, you can still do a hell of a lot of damage with the huge number of missiles. I find it works especially well against planets and planetary bases since you can see them from the start of the Planetary assault and if the planet is disabled they will automatically seek another target.