You can enter and save common transactions such as customer invoices for later use. For example, you can repeat a previous transaction several times. Using memorized transactions can save time in repetitive data-entry tasks.
Recurring invoices are set up to recur at specific periods--daily, monthly, weekly, and so on. And they recur exactly the same each time. Memorized sales invoices are meant more as templates for common sales that your customers may have. And they do not recur at regular intervals. Therefore, a monthly billing for a service contract should be set up as a recurring invoice not a memorized invoice.
Entering and using memorized sales invoices
Memorizing existing sales invoices
Using memorized sales invoices while working in the Sales/Invoicing window