What is the purpose of the 'Use General' option that can be ticked or unticked? So far I haven't seen it do anything, nor noticed any difference in my armies. What is it used for?
For your main armies always manually keep the really useful generals unticked so that you can assign them to the armies that you want to use for your current war - even the 'bad'; generals are 90% of the time better than 'no general' - you can check this by hovering over the 'no general' tab on the army detail.