You create payment plans in order to break your invoices into installments. When you create an invoice and put it on a payment plan, installments are automatically calculated based upon the definition of the plan. Traditionally, installment dates are calculated starting from the invoice date and will be spaced out based on the schedule defined in the plan. Today, you can set specific dates in the payment plan itself. When this is set, the invoice date and schedule are not taken into account when the installments are created. Instead, the date on the plan is used. See screenshot below for more information:

Availability: Dec 2015 Release