You should not use it because we tell you not to use it. ;-)
Seriously, the uvm_resource_db is the underlying mechanism that supports the uvm_config_db, it’s just that the uvm_config_db includes the notion of hierarchy so during build_phase, the higher component in the hierarchy wins if there’s a conflict. After that, it’s last-write-wins. The uvm_resource_db API is somewhat arcane and doesn’t always do what you’d expect.