My main use case for PRTG Network Monitor is to create dependencies between sensors, for example, all website check dependencies on internet connectivity. We use it for reduced downtime for our ERP system because I now catch low response times before users log tickets, and for monitoring purposes.
A specific example of how I set up dependencies between sensors is that I can acknowledge alerts and leave comments, which is very useful when working as a team. It helped me avoid downtime when a certificate was about to expire, and I have much better visibility of resource usage across all servers.
PRTG Network Monitor can monitor hardware health, not just network traffic. I caught a fan failure on a server before it caused overheating. The sensors can be paused and resumed without deleting them.
The email integration helps my team stay on top of issues because alerts directly open tickets without manual entry. It also reduced helpdesk load because we fix issues before others notice them.