It's never been clear what John Henson's fit is in the NBA.
Much like Mason Plumlee, he's a pogo stick who can rebound and finish, but he has very little offensive skill for a PF and not enough bulk to be particularly good defensively at the 5.
I know Henson's been batted around here as a potential trade target for a long time now, but I think the Celts already have a better player in Zeller.