Network monitoring is defined as the use of a system that constantly monitors a computer network for slow or failing components and that notifies the network administrator in case of outages.
Some may argue that this amounts to spying but network monitoring is spying for a good cause. In reality speaking, you might want at least one of your systems is performing network monitoring. While your other systems are performing their vital functions, it is most recommended to set aside at least one computer or set of computers to monitor network activity or in other words policing your network traffic.
Network monitoring can also be used to track the flow of visitors to and from a website which also includes statistics such as time of visit, number of pages on the site visited, and entry and exit URLs.
Network monitoring enable you to track how much disc space and network bandwidth that is using, enabling users to do capacity planning based on their usage trends.