I think Crawford is a pretty good player. He was putting up 15 ppg for the season. Also has some range, hits about 33% from three. Not a franchise player, duh, but when you're only giving up an injured Barbosa and a journeyman center in Collins, this move helps the Celtics ability to score.
Best part is that Crawford has a dirt cheap contract, like 1.2m and is under salary control for a couple of seasons before becoming an RFA.
Wait for a big man in the draft, there will be like a dozen 7 footers available.