Blair in European Armor states this on ailettes (and no it doesn't give a translation of that 14th century French bit at the end unfortunately):
"It used to be thought that their purpose was to protect the head and neck against cuts from the side, but this view can no longer be accepted. The many references to ailettes found in early 14th-century texts show quite clearly that they were invariably made of flimsy material quite unsuited for any defensive purpose. It is now generally held that their chief role was heraldic, but they seem on occasions, to have been purely ornamental. This view i supported, to quote one example only, but the following entry in the inventory of effects of Piers Gaveston, dated 1313: Item, autres diver garnementz des armes le dit Pierres, ovek les alettes garniz et frettez de perles."