pattern help for a triangle head scarf?

i want to sew myself a triangle head scarf (common in “cottagecore” fashion etc), and i know it should be simple to make it— but i also commonly see them made with an elastic band or string-style tie in back, as opposed to the whole thing being one continuous triangle shape. is there a particular reason it’s so common this way, aside from convenience? and would i need to measure/size it differently to account for that kind of shape?