HA Admission Control - Disable: Allow VM power on operations that violate availability constraints

Hi, I took over a vSphere environment recently and noticed the HA Admission Control setting is DISABLED for some reason.  It's allowing the VM power on even the resource constraints may exist.  I think this is wrong.  However, when I look at the vSphere DRS option.  It is NOT turned on. So, I'm puzzled.  If both HA and DRS are turned on, the admission control definitely should be set to ENABLE to prevent the VM power on when there is the resource constraints.  What is the affect on the DRS turning on?  Do I need to start looking into the basic requirements to turn on the DRS in order for me to enable the Admission control?  Can anyone let me know?  Thanks.