when to save an attribute?

when should an attribute be saved? Should it be saved as often as possible, or does it automatically get saved when the application quits? Also can multiple instances of the same attribute be saved to the same key?
Comments
You have to save your attribute when you need to do it... Same for load, depend on your app.
I don't think that you can do multiple instances
Best to use Save attribute just before going into the next scene.
lets say if i have an attribute in 2 different scenes can i save them to the same key?
sorry for the stupid question im just 16 :P