I have seen this technique before. She give good info on folding the fabric on grain, not using the cutting mat grid and proper rotary cutter technique. I also like how she reminded everyone not to move the ruler until you are sure the cut is correct. I must be doing something wrong, however, because I always have problems with the double fold. I use creative grids 8.5" X 24" ruler, which doesn't slip. If I'm cutting narrow strips, I use 2 rulers. A 12.5" square up ruler on the fold to maintain a 90 degree, then the long ruler to cut against. Actually, my most accurate cuts are with my Accucut Studio, but I don't have a die for every strip size!
even with the Studio cutter, however, I never cut that many layers. One miscut and you have ruined a whole buncha fabric.