CAOS aims to allow surgeon a degree of precision not possible with conventional means. Accurate positioning of implants may lead to: -

Longer life of the implant It is likely that not positioning implants in a way that distributes the forces across the joint uniformly leads to stresses both between the implanted components and between the implant and the bone. These stresses could lead to early failure of the replacement.
Optimal range of movements By placing the implants so that they match the normal position of the joint in relation to the supporting soft tissue as closely as possible, a better range of movements may be achievable.
Better joint alignment As arthritic joints wear out, they may get deformed. Navigation allows the surgeon to restore the alignment precisely. Leg length differences are less with Navigated surgery. 
Better stability One reason why joints may be unstable is because the implants are placed imprecisely, in relation to what is normal, and also in relation to the soft tissue tension. It is possible to reduce this imprecision with navigated surgery.
Decreased possibility of a revision surgery By increasing implant survival and reducing failure because of improper positioning of implants or instability, the potential for a more radical revision surgery is reduced.
Makes Minimally Invasive Surgery more accurate This means that the quicker recovery that MIS may offer, is available with less risk of less than optimal implant position.
Less Blood Loss, Less Fat Embolus These are complications that are possibly linked to passing a rod in the bone marrow space of a long bone such as the tibia or the femur. Navigated surgery, because it does not entail the use of such rods, may possibly reduce these complications.