ServiceNow notifications can sometimes be triggered close together for the same record and the same recipients, which can lead to redundant or conflicting messages. To control this, the Notification record includes a Weight field. ServiceNow documentation explains that when multiple notifications are generated for the same target table record and the recipients overlap, the system compares the notifications using the Weight value and sends only the notification with the highest weight. This allows administrators and developers to prioritize the most important notification when multiple are eligible to fire. A common example in the documentation is when an incident is updated (triggering an "commented" notification) and then closed shortly after (triggering a "closed" notification). If both would go to the same user, ServiceNow will select the one with the higher weight, ensuring users receive the most relevant final message instead of multiple emails.
This behavior is the intended purpose of Weight: reduce notification noise and prevent conflicts by giving precedence to the highest-weight notification.