Think of the walking foot as an even-feed foot. It helps both layers of fabric feed through the machine evenly, so it can be used for machine quilting to keep the layers from shifting. It's also helpful with thick or slippery fabrics. The instructions for the walking foot do actually suggest sewing only one direction - I looked after others mentioned it here. My Viking 1100 feeds a lot more evenly without the walking foot than the Bernina 1130 - not sure why that is, but it's noticeably different.