Advantages of preloader in external swf or in main timeline?

hey guys i have a quick question on preloaders (i havent found a direct answer on this in the forums)…
if youre dynamically loading swfs into an empty movie clip inside the main timeline, is it better to get the data from the empty container once the stuff loads or is it better just to put it inside each swf to be loaded? what are the advantages of doing it one or the other.
the question goes to this: can you then do anything with the values you get from the preloader in the external swf inside the main timeline?
dunno if this makes sense at all…

cheers

c