Right now you can’t use many of the functions of this new account, for the simple reason that the games that use it are not out yet. The current versions of Diablo, StarCraft and Warcraft will continue to use the old Battle.net .
But there are benefits of using the new Battle.net account you can take advantage of, right now like registering your Blizzard games, and once registered you can download those games for free. There is also an option to register for beta-tests for new Blizzard games. Who knows ? maybe you’ll get invited to test the new Diablo 3 or StarCraft 2.