I have gone over this before. But not moving Harris is one of the biggest blunders Langdon has made since taking over.
The Pistons are expected to operate as a team over the cap this summer. That means when Harris becomes a free agent this summer his $25 million will come off the books, but it won't create a single penny of new cap space. So they get a hole to fill without adding any resources to fill it because they are still over the cap. People will say bring Harris back, but with his performance in the playoffs I don't think that is a very attractive option now.
They really needed to move him for a player that had a deal that extended out past this summer. Or a guy who would be a free agent this summer they wanted back and could use his Bird rights to do so. That is how you manage a roster and the salary cap.
But the decided against all that so Harris could vibe and shoot 14% from three in the playoffs. Sweet.