Use case: you are using the cloud as an over the top WAN with edge devices in 10 or 20 or 120 cloud points of presence, spread across aws, azure, gcp, oracle, etc.. and implementing MPLS tagging to make it a small carrier-style network to overcome address overlap issues between different connecting networks. (Connecting via a variety of site-to-site technologies and gre tunneling over direct-connect/express-route.