When making cookies, you can't adjust the ratio of powdered sugar to white sugar casually, because the dough is malleable, and powdered sugar can just be improved, otherwise the cookies you make will have no patterns or the patterns will be very light. Cookies made with only white sugar will also have a grainy taste.
Of course, you can't just use sugar powder instead of white sugar. White sugar plays a crisp role in cookies. If you only use sugar powder, cookies will only be crisp, not crisp, so only the combination of white sugar and sugar powder can make good cookies.
The ductility of cookies lies in the thickness of sugar particles. The finer the sugar particles, the lower the ductility of dough, making patterned cookies, while the thicker the sugar particles, the opposite, so the thickness of sugar determines the quality of cookies.