Celts get: Pau
Lakers get: Sully, Jason Terry, Jeff Green, Courtney Lee
Why the C's do it: The time is now for the C's championship window, before KG and Pierce are done, which means rolling the dice. Pau, who played GREAT in the Olympics allows KG to play the 4, while putting Pau on the block where he belongs. It dumps Green's terrible contract, and while losing Sully is tough, its not as tough as watching the C's play .500 ball for the end of Pierce and KG's prime. This means more minutes for Wilcox and Barbosa and possibly picking up Delonte West or someone similar since they're losing a lot of guards, but a very bright side for Doc's "Guys gotta go" could be bringing in a big guy who would be top 5 in the East if played properly.
Why the Lakers do it: They only do it if they are committing to D'Antoni's style of fast paced ball. Jeff Green would thrive in this system. They get much needed shooting from Terry. Sully has proven to be the steal of the draft. Lee gives them toughness on D. It means taking on more long term salary, but it upgrades a lot of positions for them while dumping someone who is unhappy and doesn't fit with D'Antoni.
Who says no?