At the bottom of the beer, if the beer is not cut properly, it is easy to tear the paper towel when cleaning up the waste paper scraps (discharging waste). Not to mention the window box, the window was originally used to show customers the products. If the tissue paper (surface layer) is torn in that place, it will affect the appearance.

Do you mean "picking double lines" by doing double lines? If there is, the function is to prevent the bottom paper from breaking when the reverse side of the cardboard is folded (especially the white paper bottom, once broken, it will reveal the yellow-brown color of the pit paper, which is quite ugly)