In the context of an EntityContainer, it is more difficult than necessary to include a service level property or set of properties.  

For example, if we want to expose the service name as a simple string property in the entity container (i.e. as a Singleton).

We could add this to a Details entity type without a key, and then reference this via a Singleton.  Then GET get <service>/details/name. It would be more natural to simply GET <service>/name.   In another example, suppose we want to reuse this structure within other entity types.  If Details is specified as a complex type, then the natural thing is to define a scalar property detail with type Details.  However, if Details is an entity type, we instead use a scalar navigation property with attribute ContainsTarget=true and annotate with Core.AutoExpand to get the same behavior.