[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.