The benefit would come into play in regard to career flexibility, ability to specialize, and potential breadth of practice. I'd consider the IM/FM route if it were available nearby- I want the ability to specialize in an IM field down the road (if I go down that path), but would also like the training in OB and peds. A combined program gets you the ability to specialize and the ability to work with basically all patient populations for only one extra year of training, something that I find quite appealing as someone that wants to someday work in a rural environment where I might be one of the only providers in a hundred mile radius. Just figured I'd shine some light on the "why" of the IM/FM dual path, though OP could have entirely different motivations.