This card reminds me a bit of Gabite or Sunflora - all of them are Stage 1 techs that can effectively copy themselves onto the field right away (Sunshine Grace another Sunflora to evolve a Sunkern, Dragon Call another Gabite to evolve a Gible, Moon Guidance another Clefable to evolve a Clefairy). I personally think there's a bit of a flaw here in Clefable, because while the other two will perpetually search for a type of Pokemon, Clefable must be used to evolve a Pokemon, and after a certain point in the game, that no longer becomes necessary.
What decks do use evolution? Okay, there's Darkrai/Hydreigon, which is a possible, but those decklists are usually pretty tight to begin with. Empoleon could be a possibility for Clefable, to ensure they'll set up another Empoleon ASAP (which, from what I've seen, they sometimes have trouble doing). Blastoise might also have a use for this, I don't know.
It's a hard card to fit and sometimes even unnecessary to do so, but it's not something to overlook either.