In the iPad view lifecycle, what does the "window" do? Can you have more than one window for an App?
A window manages a view hierarchy and controls things such as events and first responder status. You will have multiple windows if you use the keyboard (as pointed out by Radek in the comments), UIAlerts, or if you support TV out. You could use multiple full screen windows without TV out and switch between them, just like switching the root view controller of the window, but I don't think this is done very often.