Comment by tomku

Internal scene transfer was (and still is, afaik) done using FTP servers, often very primitive ones because they had to evade detection on hacked servers. When you're racing a large game or movie from one server to another, the last thing you want is for a random disconnect to ruin it 90% of the way through, or even worse, to finish it and find that the CRCs don't match because of random corruption. It also means that you can race from multiple sources for higher speed, and like you said, use a server as a source before it's actually done downloading.