Lately, live streaming of concerts has been a terrific way for bands to connect with audiences, of course. If doing it through Hangout enables an artist to reach people they couldn't reach through, say, LiveStream, then it's a good weapon to deploy. Daria Musk used Hangoutparty.com, which appears to be an aggregator/promoter of hangouts, to both promote the event and stream it to a broad audience simultaneous with the actual hangout. She obviously got a lot of attention that she wouldn't have gotten on a LiveStream concert by virtue of being (apparently) the first artist to do this on Google+ Hangout. It is unclear whether this platform will really prove to be better then other ones out there once the novelty aspect fades away.
I will tell you this: The first couple of artists with real following to do this on Google+ will probably reap real benefits, and G+ will benefit from their having done it.
On a related note, I was talking yesterday to Israeli singer/songwriter David Broza about live streaming his August 13th all-night til sunrise concert atop Masada. We speculated on how to integrate Google+ into this. Doing a live stream from such an exotic and remote location, culminating in a fabulous sunrise, would be pretty cool. Stay tuned.