Local IdM (identity management) is for organisations wanting to manage users locally in their own administration system.
An IdM integration ensures that users and rights are automatically maintained in MitID Erhverv. This way you don't have to manage your users in two places.
With a Local IdP you can issue identities and local authenticators to your users locally while synchronizing these with MitID Erhverv.
As a user organisation, you need the option to create a test organization with test users and certificates that can be used for integration of your own systems, e.g. IdM and Local IdP.
If you are a service provider and implement other services in NemLog-in besides MitID Erhverv, you can read more about the integration test environment at NemLog-in.dk.