https://docs.servicenow.com/bundle/tokyo-servicenow-platform/page/administer/notification/task/t_CreateANotification.html
https://developer.servicenow.com/dev.do#!/learn/learning-plans/quebec/new_to_servicenow/app_store_learnv2_automatingapps_quebec_when_to_send The Weight field in an Email Notification determines which notification is sent when multiple notifications are triggered for the same record and recipients. Only the notification with the highest weight is sent. A weight value of zero means the notification is always sent when the notification's When to send criteria is met. A weight value of -1 means that no email should be sent3. Reference: Email Notification Weight