Exile is more a designer's tool than an evergreen mechanic, so I hope you learned some nuances about it today
Assuming this doesn't stop your spell from being cast, the spell 'resolves' into a permanent, which sits on your side of the battlefield
If you do, this creature gets +2/+0 until end of turn
Combine two Walls with Recurring Nightmare, and suddenly you're drawing a card for every you spend
However, there are some cases where the rule of one card copy per deck can create even more adverse situations Circu, Dimir Lobotomist Circu, Dimir Lobotomist, oddly enough, can be viable in play, even without using its last ability to stop casting cards with the same name as the exiled cards
Indulgent Aristocrat is one of those ways, giving each Vampire a +1/+1 counter for two mana and the sacrifice of a creature