Well with blowing up a star system, this makes is so that no one claims it. It's a major drawback, and by blowing up a civilization, you ultimately lose those assets, gain no power and lose an expensive warhead.
It would remove a threat, but that's really about it.
The question about warfare on the galactic scale is "What is the new ground warfare?" As we've gone from the 20th the the 21st centuries, war has been about air superiority. With space, the safety of civilizations is now dependant on spacial superiority.
This makes ground warfare questioned. While those tactics would have to be employed, it is more important to do so quickly and efficiently. This lends favor to the HK, which uses robotic forces with highly advanced AI. Ultimately, AI drones would swoop in and complete an objective without compromise. Biological soldiers, unless used as biological weapons themselves, would be obsolete.
So how is this level wafare defined, and what does it demand?