I know it's a debate that has come up quite often, but so long as the RTT organizers and Indy GTs organizers allow it, i continue to play it. The basic reasoning behind the allowance is that Daemons can't take Magical Banners from the basic rule book. (i wish I could take the Razor Standard!)
Aside from that, the build may seem a bit "boring", however it allows you to concentrate on the game basics. Maneuvering and Close Combat. Without Magic or Shooting to distract your decision making, it helps stream line your game play. It also makes for much faster turns, as there's a lot less to do. I've found that some players are unscrupulous when it comes to "time" in Tournaments when they're facing inevitable defeat.
Now in some shops and some Tournies they do insist on the inability to repeat Daemonic Banners which is perfectly fine. It saves me 150 points which i often spend on either bulking up Bloodletter units or another Herald.