Most of women would wear makeup in bathroom and it is not a good idea to open the makeup box at every use. Instead women have come up with the idea of glass cups to put their cosmetics and other tools like cotton butts into it . Therefore they dont need to open the box, take out tools and other instruments and again put them in and close the box.
Glass cups are very good useful obects to be used for such purposes. While it saves time, it is also a clean material.