Celtics will pay Memphis more than Melo's salary for taking him off our hands

Boston’s primary goal in the trade was to get under the luxury tax threshold, which likely means Greene is waived by the team before the season begins.
Boston drafted Melo in 2012 with the 22nd overall pick but they dumped him to get out of the tax.
No we're not getting the bag of Doritos for Fab.
We have to throw them in to get rid of Fab.

The Celtics also sent $1.66 million in cash to the Grizzlies to make the deal, about $349k more than Melo will make next season.

Under the rules of the new Collective Bargaining Agreement, Boston can only send out $1.54 million in any other trades through June 30. The max a team can send out this season is $3.2 million in cash, collectively.

It's common to send money in a trade to offset salary. Rarely do you see a team pay for the full contract. But in the case of Fab Melo the Celtics are not only paying Fab's full salary, but giving Memphis extra money for the trouble. So if you thought the Celtics were trading Fab Melo for a bag of Doritos you were wrong. He was traded for nothing and we're payimg his salary too  AND we're kicking in $349K in Doritos.

The Celtics made this trade for one reason and that was to get under the Luxury Tax. I'm pretty sure they could have accomplished this other ways later in the season. For example they could trade the expiring contract of Kris Humphries for a worse player making a little less. I do understand the idea of making the move to get under the tax now, so I wouldn't say it was a poor trade on Danny's part. But Memphis aren't the fools most people first thought they were when they made the deal. The Grizzlies also get a $1 million Traded Player Exception in the deal.

A few other points of note on the Celtics end:
  • Fab Melo ends up a bigger draft bust than fellow recent Ainge draftees JaJuan Johnson, J.R. Giddens and Gabe Pruitt ( drafted over Chandler Parsons, Nikola Peković and Marc Gasol respectively). 
  • It's rare that a team trades it's two highest paid all-stars (Pierce and KG) for draft picks, and is projected to not make the playoffs, AND still is flirting with the luxury tax threshold.
  • The Celtics now only have $1.54 million left to include in trades this season, which further limits their ability to dump contracts.