|I searched for this one, but I couldn't find it, so forgive me if this is a duplicate post.
Sometimes you need or want to trim off the hemlines or seams before sewing your garment. This is especially true if you are binding an edge. One of the fastest, most accurate ways to do this is with your serger, if you have one. Simply take the needles out of the machine, or if you are lazy like me and you have a forgiving fabric, just unthread the needles. Then, with the knife engaged, use the seam guide on your serger to align your raw edge, and run the machine. Voila, the allowance is gone! This takes very little time, and gives you a good clean finish.