Diagnostic log types provide details surrounding each and every action in an Azure namespace. By having this enabled, it allows the administrator to see the overview and entirety of actions performed. This is especially useful as a mechanism to not only understand ongoing activity for a particular project, but to also be alerted to any unwanted or malicious activity.
Instructions on enabling and configuring this are found from Microsoft's official documentation: https://docs.microsoft.com/en-us/azure/event-hubs/event-hubs-diagnostic-logs