Baddoo needs to hit, but if he does, he simply brings tools that other guys do not bring to bear offensively; he takes walks, he can steal bases, he's generally disruptive. Very few players on the roster can do this, and that adds value to carrying him.
It's tough because Carpenter has probably done enough this ST to make the team as well, but unless they plan on carrying just one IF on the bench, which doesn't seem likely, or unless Cabrera has a freak accident sometime between now and Opening Day, they'll have to choose between one or the other.