If I turn off NNTP (deselect "Provide news service (NNTP) from Web Crossing") does that also turn off the "Enable newsgroup (NNTP) mirroring (master switch)" option?
No. The switches are independent at this time and this setting also defaults to ON.
If you do not use NNTP you should also make sure to deselect the "Enable newsgroup (NNTP) mirroring (master switch)" to enhance performance.
If you use NNTP, but do not have a need for mirroring, you should also turn this option off.
This will be of particular value to a large site and will increase performance.
Why? Read on...
NNTP mirroring will slow a site down when there are a large number of folders, while it walks through all the folders to check for nntp settings. Plus, because folders, users, and user groups must all be checked for conflicts in email addresses, etc, everytime a new user is registered the system must walk the folders once again.