What are custom printed labels used for?

Custom printed labels are used for a variety of applications. They can be used for postal mail, as the sender or receiver. They can be used for advertisements by companies. They can be the labels of some product, for instance a packet of mints. They can be used to seal goods, or postal mail. They can be used to spread some political message, when stuck on a light post or similar. There are even more uses, too many to list them all.