Whiteside, in order to be removed from the 25-man roster to make room for the activation of Welington Castillo, had to be DFAd, as he no longer could be optioned. The Cubs hope he'll clear waivers (I'd imagine he will) so they can keep him around at Triple-A Iowa as a backup.
But the team didn't need to add anyone to the 40-man roster as a companion move. They could have left the spot open for possible upcoming trades.
Why, then, was Wada added? There's been no announcement yet, but remember this: The Cubs need someone to start one of the two games of Saturday's doubleheader. Under current rules, the Cubs can add someone to the active roster without removing anyone, for a doubleheader day.
Chris Rusin, one possible starter for one of the doubleheader games, pitched Saturday for Iowa. His turn would come up Thursday as the I-Cubs play a doubleheader against Colorado Springs.
Wada's turn in the Iowa rotation is this afternoon as the I-Cubs play a game that begins at the time this post is being published. If -- and remember, I'm just speculating here -- Wada is taken out of this game after only two or three innings or so, I think that'd be a clear signal that he'd be on target to start Saturday, probably the night game (it would be Jeff Samardzija's turn to go Saturday on normal rest).
So this could be the reason that Wada was added, so that he could simply be recalled and then sent back after the game. If this happens, he'd be making his major-league debut.
Feel free to use this thread as an I-Cubs game thread. Maybe Kris Bryant will hit another home run. Or get a hit other than a homer for the first time in his Triple-A career.