The Flash commands enable you to get information about external SWF files, load a new SWF file, and load data from a file.
You can get the size, background colour, frame number, and frame count of a SWF file all without loading it. You could use this functionality to create applications/screensavers that might catalog SWF files existing on a user's computer.
When you want to load a new SWF to replace your original movie, the Stage size of the new SWF is not taken into account. If you load a new SWF whose Stage size is different than your original movie your application window will not reflect this change. Instead the application would remain the size of the first SWF (your original movie). Using the Flash commands you can get the size of the new SWF and use Win.setClientSize to set the application window's size to that of the new SWF before it loads.