Normally, the master of the lobby controls the NPC AI and NPC Spawns. The problem is if there are sixteen players in the lobby and all of them are at different zones, then a lot of NPC will be spawned and those will be controlled by the master of the lobby. Eventually, 400+ NPCs can be alive so It will definitely impact the performance. The new design

• Every zone will have a master. The master will spawn the NPCs and control their AIs. If the master leave the zone, one of the other players in the zone will be the master.
  
• Distant NPCs will be cached on the memory and won't be spawned until the players get close to it. The point is that when the other players are in a battle in a zone, the distant players won't be simulate the war. So it won't impact the performance anymore.