The monitoring of VMware vSphere should be a combination of proactive benchmarking and reactive alarm-based actions. vCenter Server provides both methods to help you keep tabs on each of the VMs and hosts as well as the hierarchical objects in the inventory. Using both methods ensures that you aren't caught unawares of performance issues or lack of capacity.
vCenter Server provides some extensive features, such as expanded performance views and charts, for monitoring your VMs and hosts, and it greatly expands the number and types of alarms available by default. Together, these features make it much easier to manage and monitor VMware vSphere performance.