Blowing up a star

[Suicide Junkie]

A star detonator can be useful in a military sense, you just need to use it at the right time and in the right place.
Say, for example, in a border chokepoint system.

When the enemy fleet smashes through your defenses and a hundred ships start moving towards your core systems... BOOM!
Then you fight back with your new numbers advantage, and unmothball your sun creator to re-arm the trap.