I mentioned the Catalyst before: the unobtainium that makes fusion possible at very low temperatures. I posited that mankind would expand out into the universe to seek more catalyst (unless the solar power lobby won).
The assumption was that ships would use and reclaim Catalyst as they generated power. It is somewhat expensive. Besides the storage and recycling systems take up a lot of volume and mass.
With any valuable resource you will have conflict over it. Maybe not eternally but it's a good long term bet. One of the coolest ideas in space conflict is the star fighter. But those little ships can't afford the space for recycling and storing Catalyst. Therefore they have all their fuel catalyzed before launch. It's economical given the size of the ships and their short duration missions.
One of the other cool things about space battles is explosions. In the past I've said a ship probably won't explode when its reactor or drives take damage (unless you are deranged enough to use antimatter for example). This rectifies that. Now you have a big tank of fuel ready to fuse. What is its ignition method? Lasers! Missiles can catch ships without huge drives!
<<Pew! Pew! Pew!>>
(Of course I know there's no sound in a vacuum. The SFX are added to archival footage.)
Needless to say shuttles and civilian vessels have their Catalyst supply limited by safety regulations and they all use the recyclers which makes them slower than the military ships piloted by suicidally brave pilots. You don't even have to say all the enhanced fuel will go up. Make it as big a bang as you deem artistic.
Whatever, I got my big explosions.