Creating a backup is a critical step before performing an operating system upgrade. This process ensures that personal files, data, and user preferences are preserved in case of any problems that may occur during the upgrade. If any issues arise, users can restore their system to the previous state using the backup. System Restore is different as it reverts system files and settings to an earlier point in time but does not guarantee the safety of personal data. Disk Defragment only optimizes the hard drive, and Clean Install refers to installing an operating system from scratch, which would result in data loss if no backup is made.