For an agent, knowing if a user has read a message will help him/her decide if the conversation has to be marked as resolved or not.
When an agent replies to a message from the user, he/she is expecting a reply from them. In most cases, once the user's issue is resolved, the user does not get back and the team members are not sure if the issue has to be marked as resolved. Read receipts help team members figure out when a user has read the message. If a team member sees "Seen" message as below, it means the message is delivered and the recipient (user/visitor) has read their message.