There is a good reason on lifting the file on the return stroke and it has nothing to do with wear. When I come close to the desired dimension, I coat the workpiece with a magic marker. Run the file, then check the result. With practice, you can get when laying a straight edge or square there will be no light showing through. It does take practice. However, when one gets fairly good at it, you can save a lot of time. It's much quicker filing one or two edges instead of setting up the mill.