When you go to the Suppliers or Customers screen and view a transaction history, you have an option to print the view. It would be beneficial I feel to allow the addition to a total value field to be added to the end of the selected period your printing.
For example, you print a customers monthly transaction, the end of the printed report it would be useful to have their total spend (or credit) instead of having to whip the calculator out and start crunching more numbers.