I tested some things and you're right about embedded pictures.
But when you use the placeholder it doesn't.

new>add object>placeholder>change contents to image or swf
>export or publish.
close
Open again>change the content of the placeholder to another pic or swf
export or publish
You want to use the same folder for the project,so if asked
you probably choose the same folder as the project folder
This is most likely as you don't want to create xx folders to work on one project.
Now take a look at the export folder(say;index_html_files)
You'll see all previous used flashfiles and or pics in the folder.
When you publish all files get uploaded.
Now why would one use the placeholder for pics.

1-the convenience of the place holder that content can be changed in the layout but the object remains the same size.
2-have the link and or text altered through cms sytem.


Hans