Works in the NBA trade machine:
http://espn.go.com/nba/tradeMachine?tradeId=mfga7th1. Why the Pistons do it -- What they acquire in this trade are shooters and scorers. Getting rid of Monroe also allows them to play Drummond and Josh Smith in their natural positions at 5/4 and plug Green into the 3.
Crawford is also an effective scorer and 6th man for them. No commitment to keep him, and they have Green under contract control for 2.5 more years. Meanwhile Monroe is about to get VERY expensive and they'd rather move on and get a starting fit for their team. They can let Crawford walk if they don't want to keep him.
2. Why the Celtics do it -- Celtics desperately need a real 5 to plug into their lineup. Monroe + Sully gives them a legit frontcourt. Plus both big men are good passers for their position. They can continue to build a lineup that has high basketball IQ and now has the size to defend the rim. Favarani is not a starting 5, Monroe is.
Meanwhile, Stuckey gives the Celtics a sizeable expiring contract that can either be used in a trade, or just for the cap savings to sign a free agent in the future. If Monroe fits like a glove we extend him. A 'max' contract for him will only be in the 12m range, which is reasonable for a big man of his talent level.
C's would have a hole at SF, which they would use to give Wallace more minutes and maybe showcase him for a later trade. Meanwhile the upcoming draft is RICH in uber talented small forwards such as Parker and Wiggins. Also the C's could use Bass in a trade for some SF talent and free up minutes for KO/Sully.
Bottom line -- It's a fair trade. The trade machine predicts no actual change in win percentage. But hopefully the reallocation of resources allows both teams to benefit. The Pistons improve by dropping their players into natural positions by getting a legit 3. And the Celtics by giving them a legit 5 who will play intelligent ball and help protect the rim a little better. Although the C's side of the trade, the benefits are more about going forward with a slight step back in the present.