When you want to send a system, administrative, or transactional message, you may not always want to instantly alert the user or change the unread message count on a conversation.
Therefore, Stream has deisgned Silent Messages so that the channel is not marked as "unread" for users or the message count is not incremented. For example, “your ride is waiting” and “You and Jane are now matched!" are messages that would not need to send an alert.
Silent Messages are very easy to implement- all you need to do is add a silent field to the message object and set it to true and the API takes care of the rest!