Someone can come in and do the math more in detail but basically, always use CaS under DA on a single target. AoE is more situational.

DA CaS = 350 potency gain
DA SE combo over a Delirium combo = 120 potency gain

You lose the MP you'd gain from a non-DA CaS but considering it's worth about 3X the worth of a DA SE, you should always DA CaS unless you NEED MP for something.