I recently got a copy of the Farsight Enclaves, and other than the obvious advantages of having XV8's as troops, I'm really wondering why this type of force would be fielded as a stand alone, and can't see any practical use for the army as anything other than an allied detachment in support of a Tau main force... Why?
The Cons: Lackluster and expensive Signature Systems, mediocre Warlord Traits (though arguably some are better than the standard codex), No Onager Gauntlet or XV8-02 (unless you take IC's from the 8), inflexibility as to unit options and wargear ("the Eight"), vague and oddly worded rules as to which options and wargear you can take or can't take from which codex you're using, and the fact that if you play as Codex Tau, you can use Farsight and Aun'Va or Shadowsun, BUT if you play as Farsight enclave, you can't... Huh?
The Pro's: Playing as a Warlord Riptide HQ IC that can take Signature Systems, the Warscaper Drone, That node that makes all terrain within 36" of the warlord difficult/dangerous for the enemy, the Melta Blades (though the system short out rule was kind of jinky), wall of death overwatch rule, and XV8's being troops (obviously).
What I don't get: You can use units from Codex Tau, but signature systems (and does that include wargear *because there is none listed) can only be used from one or the other codex except for special rules XYZ as listed in the supplement. Confusing right from the start.
Solution?: Allied Detachment only?