A Central Alerter Server (CAS) provides a central location to configure alerts and to seamlessly browse Satellite (SAT) SAMs.
The CAS is like a central hub; it allows you to browse and monitor many SATs. A typical workflow is to log into the CAS, then browse to the SAT with the entity (database) that you want to see. In this way, you don't need to log into each SAT individually. You can also open multiple views (tabs in the web client), where each view comes from the same SAT or different SATs, allowing you to view metric data from multiple servers at once.
When you look at alerts on the CAS (Alerts tab in web client), you see alerts from many SATs. It provides a global dashboard of problems everywhere. Just like browsing SATs, the alerts that you see are governed by permissions that have been granted to your login.
Multiple CAS SAMs can be used to create a multi-tier landscape, as well. For example, each region could have a CAS, and a global CAS can sit above that level. Alerts can propagate from SATs to regional CAS to global CAS. Alert management at higher levels automatically propagate to lower levels in the hierarchy.