I often see people asking for empty milk tons but what do these people need it for?

Every now and then the milk company will come out with promotion (Tin-Exchange Program). Just last month, Friso have this Tin-Exchange Program whereas you bring a non-Friso formula milk tin when you purchase a 1.8kg tin of Friso 2/3/4, and receive Friso goodies of similar stage. Note: this program does not include 0-6 months old formula.