> Broadcast publicly. By checking "Enable Hangouts On Air," you can broadcast your live hangout—from the Google+ stream, your YouTube channel or your website—to the entire world.
> See how many viewers you’ve got. During your broadcast, you can look inside the hangout to see how many people are watching live.
> Record and re-share. Once you're off the air, we’ll upload a public recording to your YouTube channel, and to your original Google+ post. This way it's easy to share and discuss your broadcast after it's over. ..." - from the source