I like how people just automatically presume if they get a Fletchling or Bunnelby it's automatic garbage without even hecking if they have Gale Wings or Huge Power or egg moves or something!
Anyway, I keep every single pokemon I get in Wonder trade, then when I am ready to breed that pokemon I scroll through all my PC boxes and collect all the pokemon in the line I am breeding, check them for hidden abilities, egg moves, IVs, etc, then breed that out of the best (it's amazing how many times I want a particular egg move, especially chain bred egg moves, and the "garbage" pokemon (as so many people call them) have the exact egg move I am looking for, the Hidden Ability that I just couldn't find within a horde or have multiple IVs that I am looking for. After that, however, once I have bred the pokemon and I get another from the line I have already bred I just release them.