VMware HA Admission Control ensures that enough physical resources are available to meet the CPU and memory reservation requirements needed to restart the virtual machines on surviving hosts, in case there is a host failure:
Configuring cluster admission control settings
When HA Admission Control is enabled, virtual machines cannot be powered on if there are insufficient resources to meet the reservation requirements for the virtual machines that are protected in the HA cluster. The resource requirements are calculated based on the HA Admission Control policy that's selected.
In vSphere 6.7, there are three HA admission control ...
