A monitoring system for a critical application can help detect and prevent incidents that could affect the availability, integrity, and confidentiality of the application and its data. The impact of downtime could include loss of revenue, reputation, customer satisfaction, and regulatory compliance. Therefore, the cost of implementing the system should be justified by the potential savings from avoiding or minimizing these impacts.
References = CISM Review Manual, 15th Edition, page 173; An Introduction to Metrics, Monitoring, and Alerting; Business-critical applications: What are they and how do you protect them from cyberattack?