The Cavs are obviously looking like a real contender with Lebron back, but he needs some more help this season. Bennett, while having a lot of potential, likely isn't going to provide much real help, especially defensively, for Cleveland this year (and maybe not next year either). That is where Green can really help them. Green is a pretty good shooter and an above average defender. He has the versatility to play SG, SF, and PF for at least certain stretches. He would be a great fit with James and Wiggins (and even Waiters) in that regard and has the ability to take over games on occasion (when James is a bit off or they just need that extra something). Delladova is added for salary purposes. Boston does the trade to continue the youth movement and take a chance that Bennett lives up to his potential in a year or two (it also saves some money this year). Cleveland post-trade would upgrade its starting lineup by putting Green in there at SG (or SF with James at PF).