What is the reason for assigning billing plans in customer projects?

Billing plans are used for revenue planning in customer projects because they allow you to define billing dates and billing amounts for each project phase or milestone. Billing plans can also be used to create billing requests or invoices automatically based on the billing dates and amounts. Billing plans help you to plan and monitor the cash flow and profitability of your customer projects. Reference:https://help.sap.com/viewer/0c9a2f8f9c1b4a2e8b3f7d0c9b6e1d8a/2020.000/en-US/4c5f7a3e6b571014e10000000a174cb4.html