When you have an image embedded into a Photoshop project as Smart Object and you have resized it and done some work on it. How to swap for another image all the while keeping the work you've done?
Easy: Select the smart object/layer, in the Menu, go to Layer, Smart Object, Replace Contents and Select the new image.
That's it! And it's powerful. That's particularly handy when doing BD or DVD chapter menu pages with thumbnails.