It may be worth adding a warning about this on the "Create a custom columns" screen, especially as Formats is a "Quick create" template.
The Formats column causing the reading of every file in the library at startup really makes a massive difference. With 10,915 books my startup times have been about 4 minutes. Now it starts up in seconds.
It also seems to make a big difference editing metadata. I'm guessing because after editing it's refreshing part of the list, and so goes and reads a bunch of files again.
I think I added this column to my library right at the start but subsequently hid it. To be honest I forgot I had done so, and assumed it was just a default Calibre column when I was looking for custom columns today
So ever since using Calibre it really has given me a false impression as I've just assumed that Calibre was very slow starting up and slow editing metadata.
Now it seems like a speed demon
