Usefulness is quite relative. Do we really need jewelry to signal out social status to others ? I personally don't think so. (Industry only uses small amounts of gold)
That's not quite what I'm saying. Gold is intrinsically useful because you can do things with it, regardless of what those things are. Whereas literally the only thing you can do with Bitcoin is trade it to someone else.
Not anything can be a means of exchange. For that it has to have some physical properties (transportability, fungibility for example) and social properties (value !) or else you are relying on third party procedures to keep count ... or a public unfalsifiable record like a blockchain.