Duel wielding, in minecraft you can only use one hand to do everything. this limits what you can do to some degree. for instance if you want to look at a compass or a map at night, you first have to put a torch down then look at the compass. but what if you could hold a torch in one hand and a compass in the other hand, or wield a sword while still having a source of light. on the other side of the coin, you could not double wield tools that require two hands in real life (axes, shovels, ect.).