Joel Anthony landed in Boston, but not because the Celtics really wanted him. The Heat wanted to shed some salary, the Celtics wanted to pick up a draft pick or two, and the Golden State Warriors were looking for some bench scoring. A three team deal gave each team what they wanted but to make it happen the Celtics had to take on Anthony's salary.
Indications are that Joel (wisely) will pick up his $3.8M option for this year since he wouldn't get near that amount on the open market. Therefore, unless the Celtics can once again use him as a throw in as part of a trade, he's probably going to be around for at least the first part of next season.
He doesn't make any sense on a rebuilding team and his playing time after the trade reflected that. Stevens was (correctly) focused on getting the most learning experiences out of the young bigs as he could. At this point in his career I'm not sure if Anthony would get a lot of playing time on any team but at the very least he's a great character guy to have around and he's got the experience of playing on 2 Championship teams.
The team has talked about needing a "rim protector" and Anthony is known for his defense. It is always nice to have that kind of guy on the bench.
And hey, when the trade deadline comes around in February, there's always a chance that he could be on move again as a throw in. At $3.8 million, that's not a bad life when you think about it.