If you refer to monitoring networks, hardware, software, connectivity on a technical level, then it’s all about stability, scalability, security.
Mostly scalability and stability.
Traffic peaks and the like can crash your entire infrastructure if it hasn’t been set up properly. And this is easy to fake with bot traffic and other DDoS attacks aimed at your network.
Most vendors apply a series of steps to prevent that from happening. From caching layers through intrusion prevention systems, web application firewalls, offloading resources externally, etc.
System monitoring as in “network health” or operability of hardware components is also important. Some applications (and additional chips) allow for reviewing the health of hard drives or CPUs, alerting upfront in case the device is about to go offline within the next days/weeks.
It’s pretty flexible, a lot could be done in different portions of the stack.