Atrial Fibrillation is irrgular heart beat, the most common form, and when the heart fibrillates it tends to generate clots in its chambers that can cause strokes.
So coumadin is routinely used, or other anticoagulants, to reduce the risk of lung clots or strokes.
Although not mentioned in this research, anticoagulation is also recommended for people with enlarged heart/heart failure, who also are prone to clot development in the heart chambers.
Research confirms the benefits. Bleeding is the main complication of anticoagulants as you might imagine, with trauma a serious contributor, like head injuries.
http://www.sciencecodex.com/medicine_protects_against_strokes-125787