I don't know the exact issue they are referencing, but if I had to guess... these sorts of multiplayer games typically have respawning enemies that are shared w

I don't know the exact issue they are referencing, but if I had to guess... these sorts of multiplayer games typically have respawning enemies that are shared with everyone in the world. If you respawn them too slowly, then you will have tons of people standing around waiting for an enemy to respawn. A quest might require you to kill 10 of those enemies. You can see how this might be a problem. Smart games do this dynamically based on current populations.