Many applications may start with regular WAR format for web applications and migrate over to more OSGi-oriented architecture. Since SpringSource Application Platform offers several benefits to all supported deployment styles, it offers a smooth migration path. Of course, depending on your application's complexity and your experience with OSGi, you may directly start with OSGi-based architecture.
In this phase, you leverage the platform with minimal learning curve. In fact reading The SpringSource Application Platform User Guide is pretty much all that you need to do. In this phase, you gain familiarity with the SpringSource Application Platform, while preparing to take advantage of the other forms.