"net sam set workstations" fails to remove all entries to allow a user to logon to all systems.
It worked in a Samba3 PDC environment by using a null value or "" (can't remember which) such as:
net sam set workstations ""
The above appears to work but the entries are unchanged.
The entries can be edited but one can no longer remove all entries.
Very problematic since Powershell cannot be used for editing hundreds of users because Samba4 does not support web services.