Someone needs to explain to me how a guy who can't get minutes on one of the worst teams in the history of the NBA is going to make any kind of difference to the Celtics.
There seems to not be a reason why some players don't play; it isn't always because they're not good enough. Why doesn't TJ Ford play over the rookie in Indy? Why didn't Nate play for a month in NY? Why is the sky blue? Why DOES Sheed play here? Why didn't Jermaine O'Neal play in Portland?
Same for some young players. Why don't other teams pick them up when someone cuts them? Perhaps they suck, but perhaps other teams have so much dead-weight guaranteed contracts on their roster already, they don't have enough spots. Perhaps they want to save the roster spot because they're over the tax threshold. Perhaps they dont' need that position, or have other young players/projects to deal with already.
You may be right, however there are tons of reasons why decent players don't get run. He might still fill a role on another team. Perhaps they'd be better if Kiki played Battie and gave the inconsistent Yi fewer minutes, but naturally they want to develop Yi for the future, and Tony isn't part of that.