Customers make purchases from Odeon Pty Ltd by emailing their requests. On receipt of a customer's order, a sales clerk prepares a sales order. Sales orders are prenumbered and in triplicate. The sales clerk then checks that the customer's credit rating is approved by reference to a database that is kept by the Credit Manager. Once the purchase is accepted, one copy of the sales order is sent to the shipping department, one to the invoicing department, while one copy is filed in the sales department. The shipping department is responsible for sending the goods to customers. On receipt of a sales order, the shipping clerk gets the items from the warehouse, packages them, prepares a shipping order, and arranges transport. Shipping orders are prenumbered and in triplicate. One copy is sent to the customer with the goods, A second copy is sent to the invoicing department, and the third copy is filed by the shipping clerk.In the invoicing department, a clerk checks that the information on the sales order and the shipping order match, and, on that basis, prepares a sales invoice.

Required(a) Explain why segregation of duties is considered to be a useful internal control.

(b) Use an example from the case above to illustrate segregation of duties.