Staff-sweep is the Lore-master's only AoE melee attack. As one of the few damaging skills that have no induction, the skill is damagewise worth using whenever it is off cooldown, even if only fighting a single target in melee range.
Staff-sweep also has a special ability: if used while the target is under a Flank effect caused by your pet, you receive a small power over time heal. In situations where cautious power management is required (e.g. raids), it is worth saving this skill for such events.