That is interesting, but Micheal's question was, "When does preview show you everything you have done in the various panels?" In other words, how can you view all changes made in the various panels just prior to saving or printing the image? There must be some way to do that.
Panopeeper's answer is correct, and agrees with what you observed. Preview=Checked shows you everything you've done. If you think about it, this is the only thing that makes sense. If Preview=Checked only showed changes made on the current tab, it would be impossible to see what the image will look like when you hit done/open.
Preview=Unchecked only turns off changes you've made on the current tab.
To toggle between all changes you've made on/off, Set Preview=Checked, and from the drop-down menu you can change back and forth between "Image Settings" and "Custom Settings".