For example, if your singleton Frame is meant as a global user interface for your application and two are created, your application will have two Frames on the screen — quite confusing for the user.

From a more technical point of view, SCA defines the frame around business components (via a common interface definition) and enables them to communicate with each other over corporate boundaries.

The images provide the overall frame and borders for the business space, widgets, and other aspects of the user interface.