Originally Posted by GRiker
As long as there's active communication between calibre and Marvin, the screen will be on. If you switch away from Marvin, or shut off your iPad, communication will stop. This is so that your iPad doesn't go to sleep in the midst of a critical transfer of information.
These days sleep mode allows background activity to continue so it would be possible to design it to work with the screen off if Marvin supported background activity. I do not know what background activity does to performance.