If you are sewing a curved (finished) fabric edge, you'll find that without some tension-release notching, the finished edge will not lay completely flat in the final application.
Before turning the fabric layers in their right side to expose the finished curved edge, clip a few wedge notches along the curved-most area of the seam. The notches should be cut close to the stitch (about 1/8" or 1/16") but not so close that it weakens the seam or you risk accidentally slashing through the stitching.
Once the curved seam allowance is notched for tension release, turn the finished seam on its right side and iron it for a professional finish. The triangular wedge notches applied above will not only encourage the finished edge to lay flat it will also eliminate puckering and excess bulk within the seam allowance- this is especially useful when sewing decorative trims and insets within the curved seam (as shown in the image above).