I dunno. It just blows stuff up and disintegrates things!
Ok I'll get geeky with you:
The large gun on the top is for destroying ships. So, if the "authorities" were to try to use their spaceships to try and take down the Brakkian bandits, well, they'd just get shot down. The heavy armor far surpasses what local authorities could punch through.
The two smaller guns just beneath that are meant for slightly smaller targets... still pretty destructive, but easier to aim with from the Brakkian's standpoint.
Finally, I imagine the war machine would be equipped with a chaingun that ejects from the "mouth" of the creature that fires physical bullets instead of lasers/plasma shots... ideal for mass murdering lightly-armored individuals (while leaving the environment less damaged). The plasma cannons require time to recharge, so the chaingun can be used inbetween shots. Obviously, ammo is an issue both in weight and capacity, so it only gets used when needed.