Here's the thing with Giambi.
It would be one thing if, for some reason, anyone really felt like keeping a guy like Carrera would lead to him taking someone's job. Or actually competing for a spot. That's not going to happen. We know who the starters are.
Same with McGuiness... same with really everyone. They know who is going to be out there. That's why they got guys like Aviles, versatile guys that are there be the bench. The problem with McGuiness and Carrera etc, is that you're also pretty much stuck with them on your 25 all season just for the sake of keeping them.
Reality is, they've spent the money, not so much for this team to "win-it-all" now, but, for this team to compete and develop. In this "generation" of young guys, Chisenhall, Kipnis, Brantley and to a lesser extent because they are a little "older" (in experience) Santana and Cabrera are the core of this group. Zeke missed his window and they need to move forward with the group they have. If Giambi adds leadership to move them forward, that's what they need to do. The "development" of younger guys are going to be the guys that are in A ball, or whatever lower level they are at. McGuiness and Carrerra are "organizational depth" at this point, not saying that's not important, it is, but, they are most certainly not "the future."