If $user_A$ commented on a specific Answer/Question, then $user_A$ will notified via Email/Notification icon of all subsequent comments. It will be useful in most of the times but sometimes you may not willing to join in unnecessary discussions. Sadly, you can’t avoid that, On other hand $user_A$ can’t join in a discussion until $user_A$ commented on specific Answer/Question. These two features are implemented now in GO site in the form of Follow/Unfollow on every answer/question.
Thanks to @Arjun Sir