Elastic gives room for drawing out ability and recoverability of clothes. The elastic waistbands are particularly very much in use. They help you opt pants, trousers, etc. of smaller sizes than your waist, therefore making you look slimmer.
It is used to stabilize or gather knits, and it is often used to help an area of a garment stay in place. It also serves to increase the ability of garment to stretch.
Elastic is the perfect material to use for growing children, babies, or for clothes worn for comfort and meant to be kept in place.