Reyes, 33, pitched to a 3.55 ERA last year, but with less impressive peripherals. Over the past two years, Reyes has had a 4.51 xFIP in 79 innings with the Cardinals.
Still, this is one of those rare minor league signings that could actually do some good for the team as a whole. Last year, Reyes managed a solid 3.60 xFIP against lefties, which would make him a solid LOOGY candidate, and he's just a couple of years removed from a strong season with the Twins during which he put up a 2.33 ERA and 3.43 xFIP.
At the very least, Reyes could likely provide an upgrade over Hideki Okajima, who doesn't even have the numbers against lefties to play the role of LOOGY. This also gives the Sox a chance to see if he's got any of the 2008 magic in him without playing with fire at the same time.
If nothing else, he provides a slightly more reliable back-up option in the minor leagues should someone get injured than the cavalcade of rookie arms that made their way up last year.