Sacrifices use Death, although it has a low base chance of hitting. Even when not invoking Instant Death, the Death spell deals quite a bit of damage, regardless of having the Shell buff on or not. This can be a threat to low-HP characters like Hope. The Sacrifice's Anathema can inflict several status ailments. They also use Aerora.
Sacrifices are a considerable source of gil at the game's end, as they are easy to defeat in comparison to stronger enemies, such as the Adamantoise. Sacrifices also appear in larger numbers, resulting in better drop chances.