Under particular circumstances it makes sense to operate several Portal Managers:
Security issues: Portlets processing data critical to safety should be executed on a server protected against attacks.
Reusability: If serveral servers are operated in different locations, it is sufficient to make common portlets available only on one server. This makes it easier to maintain these portlets.
Load issues: Computationally intensive portlets can be executed on a separate server to improve the performance of the complete system.