Outside of Mastodon, I communicate with others almost exclusively via email; many days, I live in it. Since my MUA (Gnus) is integrated into my editor (Emacs), and my mail is in plain text, it's easy for me to manipulate.
It therefore makes sense for me to use it as a means of aggregating data.
One such example is RSS: I use r2e (rss2email) to gather RSS feeds and convert them to email, which is then sent to my local Dovecot server. I can then read them comfortably, offline.
(Of course, all the mailing lists I'm subscribed to also give me a historical archive; this isn't unique to RSS.)
Mike Gerwitz's personal Mastodon instance