Exile is a game zone generally used to remove cards more thoroughly than putting them into a graveyard. Exile effects are particularly valuable against graveyard strategies and creatures that would otherwise return after being destroyed.
Farewell can exile several categories of permanents and graveyards at once, while Prosper, Tome-Bound turns playing cards from exile into an engine of its own. Eternal Scourge demonstrates the other side of the zone by actually allowing itself to be cast from exile.
