Besides some very obvious targets like Éowyn, Arwen Undómiel, Círdan the Shipwright and Galadriel with her Mirror of Galadriel this is a really good card to circumvent all those quests and effects that make you discard cards. It works at his best in a Noldor deck, that's for sure, but it can be useful even with Legolas, Protector of Lórien, Steed of Imladris on a non - Noldor hero and so on.
Attachment. Cost: 2.
Attach to a hero.
Response: After a card is discarded from your hand, exhaust Silver Harp to return that card to your hand.
Elrond wore a mantle of grey and had a star upon his forehead, and a silver harp was in his hand... The Return of the King
The Treachery of Rhudaur #90. Spirit.
I think the best use is to save cards when Erestor would otherwise get rid of them — LEGOlas 76