For example, if you needed to repair an area of the Registry, you could load the related hive file into the Registry of another machine and then repair the problem on the remote machine. Another reason for doing this would be to change a particular part of the Registry on a remote system.
Here, you would load the user's Ntuser.dat file into Registry Editor and then make the necessary changes. The most common reason for doing this, as discussed previously, is when you must modify a user's profile to correct an issue that prevents the user from accessing or using a system. Just as you sometimes must import or export Registry data, you'll sometimes need to work with individual hive files.