I don't think you quite understand how you install to Parallels. A Windows application will always load into its own image. Whether you're running Parallels from the Sandbox or Mac HD wouldn't matter, since its virtual disk file would be the same.

Apologies for the confusion.

Maybe the simple question is....

In your opinion, is it necessary to clone my HD with the 'shared users' option in order to isolate Parallels?

Thanks

You cannot isolate parallels' data, Brent. If you want to isolate its data, you'll need to make a copy of its drive image file.