Honestly, it was for me when I started with twitter for real in 2010 (my account is from 2006, but I haven't really used it until 2010). It was unclear to me whether I should be using this as a kind of bookmark-feature as a help for me to remember tweets to get back to or whether this was a social signal I'd be sending to the author of the tweet.

The would make that much more clear to me, though of course, I have since learned how to use twitter properly (I hope).