Twitter has this thing where you can retweet something and add your own context to it. Eugen has resisted adding this to Mastodon for a long time, although I understand that it's in the works now, citing the tendency for the feature to be used as a way of getting one's followers to pile on somebody else's post. On the other hand, some communities have cited this as a very important way of how they've used the birdsite, although I don't understand how exactly and don't wish to mischaracterise their arguments.