Two different functions. The throwable (or MOB device) is put into the water to keep the MOB afloat and visible until the person left in control of the boat can return to the MOB location. At this time the lifesling is deployed to assist in recovery of the MOB.
Getting the MOB back aboard is another issue. Using a stern ladder is dangerous if there's any sea running. Safest is over the side. Whether you can use a halyard alone or need added lifting tackle depends on your boat. Can the person on board hoist the other person using just the main halyard winch? Assume the stronger of the two is in the water.