Context: you are writing a reply and it takes you a long time to achieve it (long message, or you do other things in the meantime). If someone post an answer after you start to answer but before you publish it, it can be useful to know about it: that answer may be integrated to your answer, that answer may be a warning ("the next who post will be banned"), that answer may answer the question you are answering better than you can, etc.

May be related to T63086: Flow shows new messages only after I reload the page.