Two handed casting has been popular in Scotland and Ireland for centuries. North America adopted it twenty years ago. This technique is predominantly used for casting across and down flowing rivers, small and large. Less common, but increasingly popular, is using two handed rods to cast greater distance into lakes.
Two handed casting is very popular amongst those with a shoulder injury or other impediment who still want to get good distance from their cast. Two handed casting techniques include Skagit, Spey, Scandinavian and Switch casting depending on the rivers you fish and the fish you target. Many who cast two handed just do it because it is a majestic, relaxed and fun casting style.