This parameter is applicable only in case of multisite deployment and represents the name to be used when creating the down-level ...

This parameter is applicable only in case of multisite deployment and represents the name to be used when creating the down-level client Group Policy Object in the specified domain or represents the domain in which a down-level client Group Policy Object with the default name should be created. Group Policy Object is specified in the format DOMAIN\GPO_NAME. Domain is specified in the format DOMAIN. These Group Policy Objects correspond to the down-level security groups added using the DownlevelSecurityGroup parameter
If the parameter contains only the domain name then the following default Group Policy Object name is used:  client policy for -.
A list of Group Policy Objects can be specified.