Auto resolving a battle means you miss all the carnage, but going through yet another fight you know you are going to win can get tiresome as well with all the micro-managing thrown at you by Total War.
That's where Spectator Mode comes in -- letting you turn on the AI during a battle and freely roam the battle to watch wherever the fighting is thickest. The mod also features options for changing what is controlled by AI, letting you still control your Lord for instance, or controlling your armies while the AI handles all reinforcements and summoned units.
While this is a cool mod for getting a better look at the game's combat, be advised that sometimes the AI does dumb things. So you you might end up losing units by accident!