How do you use the Banner of Rage?
It makes me think of a number of different uses.

One of these is in a unit of Knights of Nurgle. They are awesome when it comes to the -1 to hit with missile weapons and also the -1WS to enemies fighting them.
The -1WS really helps making that extra attack hit home. Also, with an extra high quality attack, maybe lances are usefull and not only ensorcelled weapons? Also, not only the Knights are affected but their horses get one attack too.
The Knights hit with 3 S6 attacks each. Can it break an enemy in the first round of combat?

I myself use the Banner of Rage on my Chosen of Nurgle armed with Shields and Halberds. They'll hit pretty hard. I wont use it on my Warriors with Great Weapons because if fortune plays against me they can come up against something that hit them first and wipe out their front rank so they can't hit back.