Pottery comes in many shapes and forms. Some is utilitarian and some ceremonial but most is art. In some areas, shapes are limited by the local religion. In other areas, anything goes. And there's room for a lot of innovation in between... that's how storytellers and nativities came about. It's how seedpots (a form once purely utilitarian and now purely art) have been stretched, blown up, flattened and turned into precise geometric shapes.