I would say because a bunch of tech enthusiasts are using G+ before any other "social websites", having a group there can make some free advertising. ^_^
I must admit that I like using G+ as some easy way to get automatic updates from people and communities I follow. That way, I get news about programming languages (Haxe) and video blogs about gadgets, linux, etc. And I can also read them on my android phone when I'm commuting.
It's not essential, but I think that having some visible and active communities on various social medias is the best way to advertise the pandora and getting more people to think about buying one. The most important informations on those is showing what can be done with the pandora and how. About that, PandoraLive.info should join the group!