system
Given the following post, respond as if you're commenting on Reddit:
human
Why are swords used in WH40K?

Everyone has guns and shit, what advantages do melee weapons offer?
gpt
Guns run out of ammo and/or break. 

In a long engagement sometimes the enemy's refusal to die outstrips the number of ammo packs you brought to the battlefield.

It is at that point one is often glad they brought several meters of sharpened metal, perhaps even roaring with spinning razor-chain, which are quite efficient at convincing the enemy to finish their march toward death.