Performance check
While monitoring your Internet services, you can set a maximum response time that your service must not exceed, otherwise it will be considered as an error.
Evidently, even if the monitoring of your web site reveals no problems, you consider that a response time of more than 10 seconds, for example, denotes a performance problem in your service and so you would like to be informed about it.
In fact, a large number of studies have shown that a net surfer who has to wait for more than 3 seconds for a response is likely to leave the website and may even end up going to a competitor; hence the importance of monitoring the "user experience" of your web site.