When would I play a Quickling?
Quickling can and should be used on your own creatures for the same reason you would use Peel from Reality: to return a creature with a useful enter-the-battlefield ability such as (at least in M15) Frost Lynx, Reclamation Sage or Hornet Queen, more usefully, because it has Flash, you can use it to save a creature that opponent is trying to hit with any removal.

So not only do you get to reuse a useful creature or save it form being destroyed or otherwise rendered useless (i.e. with Encrust or Crippling Blight), but you also get a 2/2 flier out of the deal, which you can cast any time during your opponent's turn and attack with the next turn.