An instance is a copy of an area in an MMO, usually with restricted access to a small number of players. Instancing serves many beneficial purposes:
- It saves server resources. Areas that are instanced don't even need to exist until they are needed. Uninstanced areas are up and running all the time.
- It helps preserve the sense of significance of the player's actions. If the player is told that they are the only hope for defeating the villain, and then they see numerous other people all fighting and defeating said villain (or worse, standing in line to defeat the villain), it strains willing suspension of disbelief.
- It alleviates player congestion. Uninstanced areas can have more players trying to use the area than it can support, leading to long waits; instanced areas can support player activity up to the limits of the server, which is higher than the mere limits of the area.
- Alleviating congestion also helps prevent strife between players, as some players will try and jump in ahead of the players who have been patiently waiting. This leads to anger and retribution.
- Alleviating congestion allows an MMORPG to include more solo and small group content, broadening its appeal.
The one down side to instancing that is often mentioned is that excessive or otherwise inappropriate use of instancing can lead to a world that feels 'empty' and barren of other players. This can be avoided with careful game design.
Instancing was not introduced into Final Fantasy XI until after it had been running for years. Instead, it uses pseudo-instances, where a certain number of copies (usually three) of the "instanced" area are part of the area and are up and running at all times. The pseudo-instances are widely separated from each other and the "lobby" area. Players are teleported to an available pseudo-instance when they enter the "instance" and teleported back to the lobby upon completion. If all pseudo-instances are already in use, everybody else will have to wait for one to become vacant.
Because the pseudo-instances are separated from each other by mere intra-area space rather than by zone borders, and because the Final Fantasy XI server blindly trusts whatever position the player's client reports for that player, it is possible to use certain banned third party tools to warp into a pseudo-instance already in use by other players. Other third party tools can be used to increase the draw distance to the point where the individual pseudo-instances can be seen from the lobby, floating in empty space.
The game did eventually receive an actual instance system, known to the dev team as the layer system. It is used by some Treasures of Aht Urhgan and Wings of the Goddess content. It is prone to crashing, overcrowding, and bugs, including the notorious Salvage Duplication Bug. Content known to use the layer system includes:
- Wings of the Goddess storyline missions
- Certain Campaign Ops
- Moblin Maze Mongers
- The Notorious Monster battles that occur when Sandworm sucks in players using Doomvoid