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.
Another benefit is that I then have those RSS feeds archived forever (assuming my backups last that long). Since I aggregate news sources, it gives me a personal, immutable, historical archive under my control. And I can use all my standard command line tools on it (outside of Gnus, I can simply navigate to the maildir into which Dovecot deposits the messages).
(Of course, all the mailing lists I'm subscribed to also give me a historical archive; this isn't unique to RSS.)
