In the countryside in Viet Nam, families used to be extended, i. e. three or more generations lived together in the same house. (This describes a past custom or state.)
The farmers in my home village didn't use to transport rice home on trucks. They used buffalo-driven carts. (This describes a past absence of an action, contrasted with a different past action.)
In many places in the world, people used to dye cloth with natural materials. (This describes a past practice or custom.)
Tuberculosis – TB – used to kill a lot of people. It was a fatal disease. (This describes a past frequent occurrence.)