The Master Analyzers are only available when Master Users log in. These analyzers are configured for the entire organization. In most cases the users that have configuration control can override the master settings.
Master Analyzers are very useful for medium and large organizations where an IT manager can tune Spam Sleuth for the entire organization.
For example: Say company AlphaWorks owns Spam Sleuth Enterprise and partners with company ZedWorks. A simple addition of *@ZEDWORKS.COM to the Master Friends list will keep all e-mail flowing between the new partners.