Within the context of a public event, clothes help to endow the wearer with a greater sense of themselves. You find yourself behaving differently when wearing a costume and you are often less inhibited. The costume helps to give you a new persona to project yourself from. With a ritual, a simple black robe does the opposite and is often worn as a form of anonymity. I find elaborate robes project ego and when working in a ritual context the will needs to be focused on the job in hand.