What are hems? How can they affect a garment's appearance?

Hems, although small, are super important. The biggest reason for them is that they make a garment look finished by hiding the raw edges. Sometimes, garments are left unhemmed for the exact purpose of not looking finished to match a distressed vibe. However, they are other reasons for hems besides aesthetic. Hems keep a woven material from fraying, and a knit material from rolling. Hems can also help a garment keep its shape because they keep the edges from stretching out of place. Typically, hems are sewn with a special machine, but in haute couture, they are hand sewn. Three common hand sewing stitches used for hems are the invisible slip stitch, herringbone, and whip stitch, which are all used because they are hidden on the right side of the garment. In the case of the whip and herringbone, which is called "Catch Stitch" in the diagram, they are decorative on one side which adds nice detail to a finished garment.
Images from blog.megannielson.com