"Over the years, Twitter users have turned to various solutions to save tweets. However, each have flaws compared to a native integrated feature. Retweeting and liking are invasive in that one might not want to broadcast a save, while third-party bookmarking services require more user effort.
Meanwhile, the ability to natively save tweets is needed more than ever given their increased length following the doubled character count last year."
https://9to5google.com/2018/01/18/twitter-android-bookmarks-save-tweets-feature/