Originally Posted by RAH
If you try to add a DRMed book to Calibre, it will refuse to do it. So, if you want to use Calibre to control your ebooks, you have no choice but to install the DRM-removal plugins. Otherwise, Calibre just will refuse to add the books.
This is completely untrue. You can add DRM-protected books to Calibre, store them, and send them to your reader. The only thing that you can't do if a book has DRM is convert it to another format, or edit it in any way.