User types provide additional security for a database. For example, assigning the Person user type to a name other than "unspecified" prevents an unauthorized user from creating a Group document with the same person name, adding his or her name to the group, and then accessing the database through the group name.
Designating a name as a Server or Server Group prevents a user from using the server ID at a workstation to access a database on the server. Be aware, though, that designating a name as a Server or Server Group is not a foolproof security method. It is possible for a user to create an add-in program that acts like a server and uses a server ID to access the server database from a workstation.