When I am rotary cutting multiple pieces with a ruler, it takes an extra couple seconds with every cut to find the exact mark on the ruler that I need to line the fabric with. Sometimes, I even have been known to line the fabric up on the wrong line if I am in a hurry. Then I cut the piece too small or too large.
I place a couple small post-it notes on the ruler along the line where I need to place the fabric to make the place easier and faster to find. It saves time and saves mistakes in cutting.