`save-lisp-and-die` just saves a core images which has the same global state as the current image, the saved image is executable when the `:EXECUTABLE` is `true`. However, you can only save the image for the underlying OS, eg, if you run `sbcl` in Linux, `save-lisp-and-die` will only save a Linux version.
The typical usages of `save-lisp-and-die` are, when you want to run this lisp image as a standalone exe, or when you load a lot of libs or large data set, you can save it to another image and run that image afterwards, that will save you a lot of loading time.