Have you ever looked at an expensive lace dress and thought to yourself, where are the seams?!  How is it possible to have something be completely seamless?  The answer is the applique seam, which is still a seam even though there are no visible seam allowances.  It may seem like magic but it's a couture technique, that with practice and time, you can do yourself.  If you're able to master this skill, you'll be sewing like the professionals.  This technique can be done on lace, like with my example, or you can do it with sheers, like organza, that has embroidered motifs.  These are fabrics that you don't want to have a regular seam allowance since you'll be able to see it through the layers.   When sewing applique seams, there isn't a lot of wiggle room, since you're removing all seam allowances, so make sure to sew a muslin to perfect the fit before sewing your final garment.