Agility
As described in the migration scenario, a company can react more quickly to changing business requirements when they use Microsoft development and application products. If some functionality is best kept on the mainframe, a deep integration with Windows components can still deliver an agile environment.

Supportability
Although the declining numbers of mainframe professionals remains a potential concern as long as applications remain on the mainframe, the current staff knows how to support the existing applications better than anyone else. By leaving core components of the application on the mainframe and building new functionality on Windows, you can reduce the need to retrain existing staff.

Cost Savings
Windows applications can be significantly less costly to develop, operate, and maintain than analogous mainframe ones. By developing new functionality on Windows and integrating closely with the existing components on the mainframe, you can reduce development costs and have a final environment where the new heterogeneous system has a lower TCO than it would have had if the additional functionality was added on the mainframe.

Network integration, to allow mainframe SNA devices and programs to connect efficiently to desktops and servers across routable Internet Protocol (IP) networks.

Security integration, to provide enterprise single sign-on and password synchronization to integrate the IBM mainframe security systems, such as IBM Resource Access Control Facility (RACF) , with Microsoft Windows and Active Directory.

Messaging integration, to allow IBM WebSphere MQ to integrate with solutions based on Microsoft Message Queuing (MSMQ) technology.

Data integration, so that Windows desktop or server-based applications can access mainframe data, or vice versa.

Application integration, to enable developers in either platform to call routines in an external platform and pass results between the applications.