The Symantec Endpoint Security Complete license includes the entitlement to be able to use EDR on-prem as well as EDR in cloud. You have the freedom/flexibility to choose where you deliver management with that license.
A few reasons/use cases for on-prem SEP/EDR appliance are to manage Endpoints that that may be on isolated/dark networks, if you are correlating email threat incidents from our Email Security.cloud product, if the existing SEP/EDR on-prem technology has features/functions that you are using today that may not yet be available in cloud (Host Integrity policies for example are not yet available in cloud), or if you have a preference for on-premise security vs. cloud-managed.