Every social media needs Mastodon's "personal note" feature.
That thing where you can leave a note only-you-can-see about why you followed, or why you muted, or why you blocked a profile.
I use this all the time in Mastodon to explain to future me why I took an action, and it would be great to know that while I'm wasting time remembering why I subscribed to various YouTube channels, or why I blocked various commenters.