Using an ExtraHop Command Appliance is useful when you have more than one Packet sensor (EDA) in your environment as it will give you one view of your whole environment. Documentation of how to deploy and connect the ECA to the other appliances can be found here:

https://docs.extrahop.com/current/deploy-eca-vmw/

This video will show the process of connecting the appliances (EDA/EXA/ETA) to the ECA: