This security setting determines which users and groups can run maintenance tasks on a volume, such as remote defragmentation.
Use caution when assigning this user right. Users with this user right can explore disks and extend files in to memory that contains other data. When the extended files are opened, the user might be able to read and modify the acquired data.
Computer Configuration\Windows Settings\Local Policies\User Rights Assignment
At least Windows XP SP2, Windows Server 2003
User Rights security settings are not registry keys