Why Perforate Twice?

This is information I have gathered from books and talking to others, please comment.

Beautiful lace borders are produced by perforating tools. The four needle tool, for example is used to create the delicate cut-out crosses. There are also many multi needle tools that can create unlimited patterns. However if they are used with too much pressure the parchment can be weakened and sometimes break. The answer is to perforate twice; first perforation is just to pierce the parchment and should be done on a thin cutting mat to stop the needles from going too far, the second perforation should be on a thicker mat to make deeper holes, which, in turn will be easier to cut neatly. Also embossing can be done after the first perforation when the parchment is not weakened by the cut-work.