Hi all,
when do i use an AppState?
Any time you want. Its simply a callback to update() and render() and you could for example store inside a rootNode that gets attached/shown when the state is attached and removed when its detached, containing all code to make this subsystem run. Examples are NiftyGUI, the physics system and more.
If i dont need the render() method can i use it still?
whats the reason of the postRender() method?
Yeah, you dont have to use the methods when you dont need/understand them. post render is for stuff that happens… post rendering 
For example the physics thread gets stopped here when its running in parallel to rendering.