As you might know Eclipse e4 decouples the application model from the rendering engines. For example you have a MPart model element which describes that the application should display a certain UI element (view) in your application. How this model element is drawn is determined by the renderer.
Another very nice thing about the renderer framework and the model is that the e4 application model can get extended and that you can define your own renderer for your own model element.
For example you can define a model element “GoogleMap” which will be renderered via your own renderer as a Google Map (using the SWT Browser widget).