One of the things that makes JSF different from other approaches to server-side Java web development is that it offers a much higher level of abstraction and transparently maintains UI state. While this is valuable is making web development feel like more traditional pure MVC UI development (think Swing, AWT or JavaFX), maintaining UI state is not always necessary. In fact, having a stateless view can be a valuable optimization technique as long as you design for it and can afford to do it. In recognition to this fact, JSF 2.2 allows a view to be marked stateless. Ed Burns discussed this feature towards the beginning of his JavaOne 2013 talk titled JSF 2.2 New Features in Context (see embedded video below):
Beyond the video, Thomas Asel provides a detailed explanation of the feature and it's motivation. It's definitely worth a read if you are a JSF user. The entry also references a number of useful resources on the feature.