Which of the following is NOT an impact on IT infrastructure planning?

Purchasing unnecessary software is indeed not considered an impact on IT infrastructure planning in the same way that the other options are. When planning IT infrastructure, the focus is typically on ensuring that the organization has the right tools and resources to support its operations efficiently and securely.

Installing and testing hardware is a crucial step in preparing an effective IT infrastructure, as it involves ensuring that all physical components function correctly and integrate seamlessly with existing systems. Implementing regular data backups is another vital aspect, as it protects data integrity and ensures continuity in case of data loss. Maintaining system security is essential for safeguarding organizational assets and protecting sensitive information from potential threats.

In contrast, purchasing unnecessary software does not contribute to a well-planned IT infrastructure. This action can lead to wasted resources, increased costs, and potential complications in system integration, as unnecessary software may not align with the organization's operational needs or strategic goals. Therefore, while all other options focus on enhancing or protecting the IT infrastructure, purchasing unnecessary software detracts from effective planning.