Why would a recipe call for bone-in, skin-on chicken and then never use the bone/skin?
Bone in = the breast plate is still there.  The ribs would typically be removed because in slow cooking the rib bones often have a habit of coming loose and being an annoyance or even a choking hazard while adding little or nothing to the taste.  Leaving the breast plate however is referred to by many as cooking on the crown.  Cooking on the crown is considered by many to give a better flavor, be it poultry, beef, pork, or whatever.  Additional, with slow cooking, the cartilage and bone may add some thickening effect to your broth.