What are real world advantages, if any, to duel wielding firearms?

Everyone is familiar with duel wielding guns from video games and action movies. I was wondering if this is actually viable in a combat situation. Obvious advantages would be being able to aim at two targets at once and having double the ammo, but it is even worth the trade of less accuracy, less recoil control and longer reloads? Also, is it even possible to duel wield non pistol smgs like the UMP, MP5 or MAC10 and be able to hit something?