Sometimes programs crashes and take then over 90% of your CPU usage. That slows your system down can and other programs won’t start anymore.
The CPU monitor controls the usage of your CPU and informs you if the usage comes over specified limit. So can be sure that your system is in perfect condition all the time.
In addition you can execute a task if the usage comes over the limit, i.e. you can terminate the program which causes the high CPU usage.