I'll try putting it as simply as I can, the way I understand those terms.
— Powering Up (A.K.A. Staking) gives you as a curator the power to highlight any chosen content. That power is equal to your share of all the potential attention that content can get. That way, the curator is also acknowledged as an influencer, alongside the author. Like in traditional media — influencers actually reach a new audience thanks to the audience they already have. But here, stake matters instead of the sheer number of votes.
— Delegating is like entrusting your funds to somebody who actively moves them around for you. Or for themselves... That depends on your arrangement. Some people delegate in order to reward, i.e. empower, somebody else. To let them make the influencing choices. Anyway, all kinds of reasons here but that's the result of it.