I also find it more convenient to use Send to Kindle than to connect the Kindle to the computer for sending from Calibre.
Additionally, I also manage my mother's ebooks - she uses the Kindle app on my old 1st generation iPad and it's considerably easier for me to send her books to her iPad Kindle app with Send to Kindle than getting the books to her in any other way.
I use an eInk Kindle, so the personal documents thing isn't an issue.
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