In effect, though, sending Assad "down to the minors" has largely been a semantic effort recently as a way to keep an extra pitcher around without needing to play the DL games (well, play them as much, hi Cabrera). Assad has options, so use the options to gain a roster spot. He likely didn't miss any major league time in his last stint down it was so short.
I'm sure the next labor agreement is going to have some fun wrinkles to it too, but for now, this is the built in effect of the option system, and that's really the only reason Assad is bouncing around.