I find that using auto resolve helps me think about where I am keeping my good generals. The auto resolve seems to give them credit for being more tactically aware and so gives them better auto resolution results.

Also, I tend to play through the strategy game more quickly than I should and make mistakes and act sloppily in most regards as I know I can pick up the slack later on the tactical game. If you decide to only auto resolve though you really have to maximise the strategic game as you will get no favours in the tactical. To that end I find it to be quite a useful trainer for the strategy game.

If I am playing properly though I fight every battle (except daft wee sieges).