I find armies really useful in the both the nutcracker and defense rolls. If available an infantry army is great for my guarding artillery stacks. Mainly because I get really paranoid about what an AI would do if it captured a 30 piece artillery stack . One thing I did wonder about was why people (often seen this while SG lurking) fill their armies with elite units as opposed to vetrans? I often put in Elite* units as they can't produce another leader and will lose their extra bar if they upgrade (anyone know if they regain the ability to produce leaders then?). I think the elite units are far more useful 'leader fishing' rather than increasing an army from 12-15/16-20Hp - which I don't think makes that much difference to their survivability or power.