Some mp3s for my soundtracks are available from the artists as downloads. It would be nice to keep a copy of the song on the site, but lots of songs are more than 5MB. I'm going to have to hotlink to someone else's server, which isn't cool but the only way around the size limit.
File storage on full-fledged servers isn't nearly as cheap as file storage on something like Amazon's S3 service. I might look there for large files.
We may also add a configuration option to use S3 with wagn, but that would mean sacrificing file security (other than security through obscurity, which is pretty flawed)
So you'd separate the site server from the media server, basically.