The Dodgers dealt Dustin May in the final minutes before the trade deadline, sending him to a familiar trade partner in the Red Sox for outfield prospects James Tibbs III and Zach Ehrhard. In doing so, the Dodgers basically looked at their two options for sixth starters — May and Emmet Sheehan — and decided that Sheehan would be a better bet through the rest of the season.
There were a lot of practical reasons to trade May. He's a free agent at the end of the year, and the Dodgers probably figured that they should get as much future value out of him as possible before his departure.