-It prevents raveling of woven fabrics, especially during heavy use and laundering.
-It helps a garment maintain its shape.
-It makes the garment more durable.
-It makes your garment neat and professional looking.
My tailoring instructor told us that our garment should look so good on the inside, that if we accidentally put it on inside out no one would notice. There are many seam finishing techniques and stitches out there, especially for knits, but everyone should be able to manage at least one of these 3 general purpose seam finishes.
Once you are sure the garment fits well, use a pair of pinking shears to trim the raw edges. That's all there is to it!
#2- Zig Zag
This is a great finish for many fabrics. Set your machine to a very short length zig zag stitch. When working on delicate fabrics that ravel easily and are otherwise hard to handle, I press the seam allowances to one side rather than open, and zig zag the edges together. If you have your stitch set small enough, you can actually get the machine to roll the raw edge. I have also used a tight zigzag finish to roll sheer hems. Pressing with starch or vinegar spray prior to finishing lightweight fabrics, especially hems, will result in a better end product.
#3 Mock French Seam