Originally Posted by tilleydog
The main reason is that you can edit at the Main Gui page instead of opening each book entry up to add the ISBN. Currently I have a couple of thousand PDF files imported for which I have the ISBN numbers in an excel spreadsheet. I can sort the files in Calibre by their series type and would be able to add the isbn much quicker than opening each record. Its still time consuming but it goes faster than opening each record. I tried to update the metadata.db using sql queries but calibre wouldn't read it afterwords. It was a good thing I made a copy before starting.
Let me guess; you scanned all your books to PDF. I'm doing the same thing and I'm having to put my ISBN in manually as I put each book into Calibre. Since I'm in the process of scanning my books and put each one into calibre as I complete the scanning process, it doesn't seem like such a chore since, after downloading the metadata, I usually have to do a few tweaks while I'm in the edit window anyway.