Being placed on the DL is different than a supersub that takes over when I guy needs a blow every five days. I answered that in my very last post. You can call up Sam Travis long term, but you aren't going to park him on the bench if there isn't a consistent role for him. If a guy needs a rest or is DTD, Holt is the perfect fit. If a longer term option is needed, you get a guy from Pawtucket.
Right now, Marco is a negative WAR player. He may be better in the future, but I believe you let the former All Star get the playing time before an unproven guy who only OPS'd 787 in AAA last year.
Per the Tribune on Marco: If you could have a player who hit .294/.357/.373 and played acceptable middle-infield defense, you'd probably think of that as a player worthy of a spot on a major league roster. And in most cases, you'd be right. But the Red Sox are not currently most cases. They flaunt four-win (or better) players at both middle-infield spots, and third base is occupied by one high-salary player and one gritty, team-favorite utility player.
The Sox love Holt.