I don't even really know why they put the graphic in the game to be honest, its like a big golden explosion out of your druids head. I dunno, it just does not seem very "Druidlike" to me, and frankly I don't really see any need for it to have been added?
Was it so other people knew you used it? Usually in raid situations or pvp your partners/raid members know when you are going to use stampeding roar so thats kind of silly.