Overedge stitches like serging and zigzag are the fastest, easiest and thus, most commonly used to finish seam allowance edges. The beauty of both of these stitches is that they provide an effective way to contain fraying fabric edges without adding bulk or jeopardizing the seam's flexibility and movement.
If you have an overlock sewing machine, serging or an overlock stitch) will be the technique you use to encase seam allowance edge. If not, a zigzag on your home sewing machine will work just as well. Both of these stitches have various setting to choose from to control both length and density. You should choose the stitch's density and length based on your fabric- mainly its thickness and how much it frays.
If working with a lighter, thinner fabric that frays significantly when cut, use a denser, medium length stitch. A stitch that is dense contains fraying more efficiently and if not too long it creates less tension in the finished seam when working with thin materials.
If finishing thick, bulky fabric edges use a less dense stitch (if the fabric doesn't fray too much) and a longer stitch length. The longer stitch will encase the thick fabric edges more efficiently, connecting to the fabric edge more durably. If the thick, heavy fabric frays quite significantly, increase the stitch density maintaining the longer length- this setting is especially helpful for thick loosley-woven fabrics.