The Mosaic Moments Quick Glance Guide is a great tool for previewing before making cuts using the Mosaic Moments page layout system. As shown in Designing Photo Mosaics and More - page 93.
The top grid area is for previewing a 4x6 photo before cutting into 1" squares. The quick glance guide helps you see how the image will generally look cut into 1" squares or if you will be cutting through things you don't want to cut through - like someone's face.
The bottom of the quick glance guide is used to preview larger pieces of the photo that fits the grid. The bottom grid lines include the "gaps" that are between the squares (1/8" gaps).