Games Workshop have posted a new Lord of the Rings Tactica articles examining the uses of the Nazgûl.
From their website:
There’s no disputing the fact that the Ringwraiths are an ominous presence in the story of The Lord of the Rings, and the same can be said of their presence on the battlefields of The Lord of the Rings Strategy Battle Game. Whether in the skirmish game or an all-out War of the Ring battle a single Nazgûl has the power and potential to completely change the flow of events, and when acting in a group they can be utterly devastating.
When choosing your armies for The Lord of the Rings, there is a wealth of different options for you to include, but one of the constants is that almost every Evil force has access to the Nazgûl (only Sharkey’s Rogues don’t). Because of this, there’s no reason not to include a Ringwraith or two in your collection – and when occasion demands, you can include it into your force, ready for action.