"Servers" list in client config

Hi,

We're Netbackup 7.5, mixed Unix and Windows.

In the admin console if I add a server in the "Servers that can access the currently selected host" window, what am I enabling?

Is it allowing the servers listed to act as media servers and back the client up?

Is it also allowing them access to the client when the server is running the Admin Console and wants to query the client?

Also, if I look in the registry on the client, the Master server always shows at the beginning of the key HKEY_LOCAL_MACHINE\SOFTWARE\VERITAS\NetBackup\CurrentVersion\Config\Server. But it is not listed on the client object in "Servers that can access the currently selected host". Why is that?