Rules based on tags reference datastore tags that you associate with specific datastores. You can apply more than one tag to a datastore.
Typically, tags serve the following purposes:
Attach a broad storage-level definition to datastores that are not represented by any storage providers, for example, VMFS and NFS datastores.
Encode policy-relevant information that is not advertised through vSphere API for Storage Awareness (VASA), such as geographical location or administrative group.
Similar to storage-specific services, all tags associated with datastores appear in the VM Storage Policies interface. You can use the tags when you define rules for the storage policies.