He was the youngest of the 1B/DH logjam and they needed to see if they had anything in Sheets and Burger. The answer on both of them seems to be no, so Vaughn should DH when healthy.
I know people keep saying this, but the Sox FO is incredibly stupid, and what if he goes on a run of BABIP luck where he pitches well for a few starts before getting lit up?
I don't think Cueto is any better than Keuchel but I'd rather them launch Keuchel and go with Cueto just so they don't have to worry about any commitments for next year.
It's worth the $4.2M or whatever Cueto will make to not have Keuchel on the books next year. Consider it part of his buyout.