The type of plug-ins I used for FFXI, like recast, yarnball, and spellcast were unfair in so far as they gave you an edge over other players. Their entire purpose was to make you more efficient. Spellcast was certainly the most broken one that I used because it managed all the gear swapping associated with each spell. It let you do far more complicated things than the in-game macros allowed and with speed that a player would not be physically capable of making (swapping in different gear sets before, during, and after casting specific spells, for example), but it only maximized your potential without hurting others directly. It's an edge, certainly, but not one that broke any of the game's coding.