I know some have suggested doing that but it does not work. Importing the reg file does not restore the registry it just adds the entries in the reg file to the registry. It does not remove the old entries. They are still there.
Yes, it can be beneficial if you deleted a whole section of the registry and you want it back.
If you are really are having registry problems, there is the possibility that the importing functions will not work anyway.
I also think that you are going to have problems exporting and importing such huge files.
Windows 7 also has the bad habit of blocking what it does not think you should add, change, or remove so even if it seems to have imported properly when you look at the actual entries you may find that some entries did not change or import.