Final answer:
When auditing a company's internal controls for computer processing, 'The cost/benefit of data processing operations' is of the least importance, as auditors are more focused on the accuracy and security of financial data.
Step-by-step explanation:
The question is asking which factor would be of least importance to an auditor when considering the internal control systems of a company that processes its transactions using computers. Among the options, The cost/benefit of data processing operations (D) is likely to be the least important. Auditors are primarily concerned with the accuracy, integrity, and security of financial data. Therefore, they focus on issues such as segregation of duties (A), control over source documents (B), and the documentation maintained for accounting applications (C). These are critical for preventing fraud and ensuring that financial information is reliable. The cost/benefit analysis of data processing operations is more related to management decision-making rather than the audit of internal controls.