It really depends on the content you are distributing too, as streaming can really reduce bandwidth. Streaming works much better if you are sending very long recordings as most people won't download the whole thing if you stream it. We found that it really reduced our bandwidth when we moved some long video's to stream rather than using progressive download.
Streaming doesn't automatically protected your content, it at best obscures it a bit.
Flash has options for encrypting content as it's sent, not sure if that's been broken yet or not. And if someone -really- wants the content, they'll get it anyway.
Exactly, in fact nothing you can do can protect your content (well short of not letting them view it). As anyone can get a screen recorder and capture it.