He broke his foot so the Cavs moved him to save 3 million in luxury tax and open a roster spot for the trade deadline and buy out market a month later (I believe they used that spot in Dahntay Jones) I assume since he was injured Orlando cut him rather than keep him on the roster. It was your classic salary dump where you acquire the player and cash and then you cut him for the team over the tax. If he doesn't break his foot maybe it works out differently.
did some research
Looks like lebron forced the cavs to dump Joe Harris to sign either McRae or Dahntay Jones. Lebron era: Pack up any young player, and out he goes.
Again he broke his foot and was out for the year. For a team that is competing for a championship having a dead roster spot and paying 3 times that salary in luxury tax makes no sense at all to keep that player. The Cavs went on to win the title that season and got useful playoff minutes from Dahntay Jones, who wouldn't have been on the roster but for the Cavs moving Harris earlier that year (and when I say useful, I mean he actually played, something Harris would not have done since he broke his foot).
Here was then Cavs coach Blatt on the trade
"Obviously with Joe having season-ending surgery, Griff [Cavs GM David Griffin], who is always working, was looking as always to create flexibility for possible opportunities going forward," Cavs coach David Blatt said before Cleveland played the Dallas Mavericks on Tuesday. "Joe was a real good member of the team. He was a guy we all liked having on our team. A guy I really enjoyed coaching. A terrific teammate and a guy with a real future, I believe, in this league. It's one of those things that you wish it didn't have to happen, but it's understandable under the circumstances why."
http://www.espn.com/nba/story/_/id/14557501/cleveland-cavaliers-trade-joe-harris-orlando-magicHad he not broken his foot, he certainly wouldn't have been traded when he was and the manner he was traded, but them the breaks (pun intended).