What are some scenarios in which "Automatic (metadata) Management would be used?

[Dal Bhat]

The setting description says it will keep the library and device metadata in sync.

What might change that such that I'd want that to be reflected in the Kindle copy?

Do you use that setting, and why?

[Sirtel]

First, you can't do it with a Kindle, because Calibre can't access its database. It works with a Kobo, because its OS is open.

I do use that setting, because it means the metadata, including comments (the synopsis), series info and collections, transfers to my Kobos automatically, without my needing to do any manual work on the device (like setting up collections). And every time I change metadata in Calibre (title, author, cover, series, comments, rearrange the collections data) the changes again automatically transfer to my Kobos when I next connect them to Calibre. I won't have to resend the books to get the changes to my Kobos.

[Dal Bhat]

Originally Posted by Sirtel

First, you can't do it with a Kindle, because Calibre can't access its database.

That answers that for this Kindle user. Thank you.