Peter has some solid thoughts here on some subtle uses of things including likes, favorites, and bookmarks. I particularly like the way he separates out and describes the “vote” intent of likes on various platforms.
Somewhat like him, I’m bookmarking things I’d like to read privately on the back end of my site, and then only selectively posting them as read posts when I’ve done that. Archiving them to the Internet Archive has been useful for cutting down on the data I’m keeping, but saving them does allow me to browse through my commonplace book frequently when I need to find something and couldn’t find it otherwise.
Some of this reminds me of the way I use the “star” functionality on Twitter (I still think of it as a star and not a heart). I don’t typically use it to mean anything in particular on Twitter itself. Instead I’m using that functionality in conjunction with an IFTTT recipe to bookmark things I’d like to read later. So in a larger sense, I’m using Twitter as a headline feed reader and marking all the things I’d like to come back and read at a later time.
Once in a blue moon, during a chat with others on Twitter, I may use the heart as an indicator to the other party that I’ve seen/read their post, particularly when I don’t intend to reply to the last in a chain of conversation. This type of ephemera or digital exhaust generally isn’t something I find useful for keeping in the long term, so like Peter I typically don’t keep/archive them on my site.
For those who haven’t read them yet, Sebastiaan Andewe has a recent article covering similar ground: Thinking about bookmarks and likes on the IndieWeb.
I find these discussions useful for thinking through what I’m doing on my own site and refining how I use it as well.