Actually, 3 most useful and critical Monitor features still have not been mentioned
accidentally, these features is something you cannot get by using native tools (vSphere Client).
Those must have features are:
1. Snapshot monitoring and alerting (including abandoned and hidden snapshots that cannot be seen in vSphere Client).
2. Guest disk space monitoring and alerting.
3. Huge number of predefined alerts (based on years of gathering best practices from VMware environments), and knowledge base with resolution details for each alert.