Sam Cassell seems to be providing Danny Ainge with some roster flexibility as well as some unofficial coaching. I suspect that unofficial coaching may become official by the trade deadline, thus allowing Danny the flexibility to sign a free agent and make a trade.
This arrangement is a win/win in that it allows Sam to be with a terrific team, ease his way into the realm of coaching, and make a little more money as a player. It is good for the team because of the aforementioned flexibility. The Celtics have an insurance policy if someone goes down, they have some experience and added locker room leadership, and roster flexibility if they need to "cut" him (and make him an official coach) when they want to add another player via trade or free agency.
I doubt he ever sees the floor this season as a player. Unless... if there is an injury to Rondo or one of the other guards as the season wears down, then Sam will be brought back as a player.
Do any of you have a different take?