Originally Posted by Starson17
It sounds useful to me. What I've been doing without this feature is to move the library. Calibre moves everything it knows about, deletes the associated folders in the library, leaving only the books that are not in the database. I then add back into Calibre all the leftover folders/books. It's a lot of steps.
Another way of looking at this might be to move all the files that Calibre does NOT know about to another location initially. This could be the first step in deciding what to do about automating adding them back. A side effect is that it would handle the case where a user has mixed up Calibre folders and none-Calibre ones as all the none-Calibre ones would then be moved out.