Network Watcher: A regional service that enables you to monitor and diagnose conditions at a network scenario level in Azure. You can turn NSG flow logs on and off with Network Watcher.
Network security group (NSG) flow logs is a feature of Azure Network Watcher that allows you to log information about IP traffic flowing through an NSG.
Why use NSG Flow Logs?
It is vital to monitor, manage, and know your own network for uncompromised security, compliance, and performance.
Common use cases include Network Monitoring: Identify unknown or undesired traffic. Monitor traffic levels and bandwidth consumption. Filter flow logs by IP and port to understand application behavior.