Obviously Sweeney did not have a good year with the Red Sox in 2012. He started out strong, but faded fast and, perhaps in part thanks to a concussion, he was pretty hard to watch game after game by the middle of the season. It was almost a mercy when he finally knocked himself out for the rest of the year by breaking his hand punching a door.
If Sweeney grated last year, though, that doesn't make this a bad idea. As we know, Ryan Kalish is gone, and with him the insurance plan for Daniel Nava as our left-handed hitting outfielder, or just a versatile fifth outfielder period. Sweeney can play anywhere in the outfield, hits left-handed (though "hits" is being a bit generous), and most important of all is here on a minor league deal. That means he doesn't effect the payroll unless he's good enough to get promoted, and doesn't force the Sox into assigning him a roster spot. The bad news is that it comes with an opt-out, so if he looks good in spring training (or possibly even if he doesn't), the Sox will have to bring him up to keep him aboard.
Sweeney has earned no great love in Boston, but depth is depth, and frankly he has more upside than most guys who would fill this role, even if it's exceedingly unlikely we'll ever see it.