For (1) On a system with two interfaces; say eth0 and eth1 - when they are set with IP addresses belonging to the same subnet, we need a way to set the routing priorities on the routing table. Otherwise, kernel adds two default routes for the same subnet on both interfaces, and its not guaranteed as which interface is actually responding to the incoming packets. Setting the route priorities is achieved via the 'Metric' value in the routing table. For a dynamic address assignment(eg: DHCPv4), networkd assigns 1024 as the metric value by default. There is currently no way to set this Metric value for a Static configuration via Redfish PATCH command on EthernetInterface.
For (2) Static route configuration interface will help in setting up the system's network in such a way that, user can add another device(say a redfish client) to reach the system via a specific controlled route, other than using the default routes. This enables to have client and server at two different geo locations & two independent network zones.