I think bsbs are useful. First, if you build a mini blender for 25 points you grant him +1 car and an extra banner for blood and glory. It makes vampiric and ethereal units within range less crumbly. Finally, a wight king bsb is tough and lets you put any magic banner where needed. Ghouls with a razor standard are more effective. Grave guard with both the razor and barrow banners even more. I agree you got to be careful where you put them, but they have their uses.