It's pretty obvious, if you look at the second image in the stack, that a "Mistake" has been made. Take a look at the screen captures of different stages of creation of today's image. In the first panel a simple pano was made out of three original images. To illustrate the point a deliberate "mistake" was made right after the pano was made. Obviously, the word mistake wouldn't appear in a typical image, but it could be a small piece of rubbish, a double or smeared person walking by, or any number of other things that would detract for the overall image. In this case, the mistake goes unnoticed until the very end of the processing. The image is complete, with adjustments made, the image sharpened and the final vignette applied. Then the mistake was noticed. Through the magic of Smart Objects, all the work done to the image is not lost. No Layers had to be recreated, no Hue/Saturation Adjustment Layers had to be discarded. Double clicking on the base Smart Object opens the Smart Object beneath, which opens the underlying Smart Object, which, eventually, takes us back to the original components making up the pano. We can stop anywhere along the process and make changes. The "secret" to nested Smart Layers is Save and Close, Save and Close, Save and Close your way back up to the top level. If you started out in Adobe Photoshop Lightroom 3 you can hit Save once more and it will produce a PSD file next to the original set of images. It'll be named XYZ123.edit.psd. You'll be able to reopen it at any time and make any modifications needed at any point in the processing. My thoughts can be found by hitting the "read more".
If you currently use CTRL/ALT/Shift/E (CASE) to make a composite copy of the layers you've been working on, you'll find the Smart Object route to be much more flexible. Once you've used CASE you've put a line in the sand. You're saying "I know I won't need to change anything below this point". That's great, if you're right 100% of the time. If you've put time into developing an image and decide anything needs to be changed below the CASE Layer you'll have to redo everything above the CASE Layer. Unless you've made scrupulous notes you may not remember that the Brightness/Contrast Adjustment Layer clipped to the seventeenth pixel level change you made was +17 and -3. Using the Smart Object nesting method you don't have to. Go back as far as you need to, make the change you want and then walk yourself (Save, Close, Save, Close, etc.) back up to either the end or to the point you left off. You have total flexibility.