Why does the Place Monthly Order screen show 2 or more rows for 1 customer contract?

QWhy does the Place Monthly Order screen show 2 or more rows for 1 customer contract?

In the Place Monthly Order screen, orders can be placed per customer contract and order due date and delivery to/ sub customer.

If a contract has parts for 15th and 20th due date, the system will give the option to place orders for both due dates at the same time.