I just read a comment over on one of the articles about this that really made sense after I a little thought. It basically said the Celtics traded away Cassell and cash for the pick (cash<>pick), expecting the Kings to waive Cassell. After that, the Celtics would be able to sign Cassell as an assistant coach, so in the end this whole trade just allows the Celtics to take Cassell off of the salary cap for players while still doing what he was doing before the trade.
XI Wiki



