Xinerama allows a screen to span multiple monitors in a freely configurable geometry. In such a setting, maximizing a window would ideally not grow it to fill the whole screen, but only the monitor it is shown on. There are of course borderline cases for windows crossing monitor boundaries, and 'real' maximization to the full screen may sometimes be useful. A shaded window typically shows only the titlebar, the client window is hidden, thus shading is not useful for windows which are not decorated with a titlebar. A typical example of a transient window is a dialog.
Some dialogs can be open for a long time, while the user continues to work in the main window.
Other dialogs have to be closed before the user can continue to work in the main window. This property is called modality. The Window Manager may offer to arrange the managed windows on a desktop that is larger than the root window. The screen functions as a viewport on this large desktop. Moving the viewport is achieved by moving all managed windows in the opposite direction.