Give a customer a single document summarizing everything they owe.

Bookkeepers and AR staff following up on outstanding balances
Customer Statements produce a period summary for one customer - every invoice, payment, and credit memo in date order with a running balance. It is the document you hand (or email) to a customer who asks 'what do I still owe you.'
See how Customer Statements fits into a plan on pricing, or how Count My Bucks compares to QuickBooks.