Some skills now do extra damage if used when sneaking. Being outside of the combat is actually very good because enemies freeze once combat starts and an allied turn comes up, letting you position your rogue at will. That's half of the benefit of using Guerrilla.
Because of AP costs, once in combat, Guerrilla is only particularly worthwhile when dual-wielding. When single-wielding, Sneaking is only useful as the final action in your turn (and that relies on enemies not turning around to look for you).
