1) The document discusses how hashtags on social media, particularly Twitter, are used to group messages and topics. By including a hashtag, users can connect their tweets to others on the same topic. 2) It provides the example of the destructive #NekNominate challenge in 2014 and how a response video with the hashtag #ChangeOneThing was able to redirect the conversation. 3) Predicting which hashtags will become popular on Twitter is important economically due to the platform's influence. Hashtags are analyzed based on their spread through users' social connections and semantic similarities to other tags.