Fabric cutting details - what is the purpose of facings?

A facing is a piece of fabric used to finish raw edges of a garment at open areas, such as the neckline, armholes, and front and back plackets or openings. A facing may be a separate pattern piece to be added to the garment or an extension of the pattern piece itself. Facings are usually sewn face-down onto the pattern piece, then clipped and turned toward the inside of the garment.