Final answer:
After extending a primary NTFS-formatted partition with unallocated space, it typically becomes usable immediately without further action. A restart may be required only if the extension isn't recognized instantly by the system.
Step-by-step explanation:
When a user wants to extend a primary partition formatted with the NTFS file system with the unallocated space on the hard disk, there is generally no additional action required to make it usable after the extension is complete.
After extending a primary partition, the user needs to initialize and format the new partition to make it usable by following the steps in Disk Management.The NTFS file system is dynamic and can expand to fill the new space without the need for additional formatting or intervention. However, if the disk management tool used to extend the partition does not refresh the system view or there is some issue with the extension, the user may need to restart the computer for the changes to take effect and for the operating system to recognize the newly allocated space properly.