I am all for lessening the micromanagement but how is defend better than preach? Doesn't everything (unless in a Fortress) just defend if the province is attacked unless it's been given a specific order that stops them? I mean mages in a lab defend if the province is attacked don't they? Don't blood hunters 'defend' too and Patrollers? So what is the benefit of not preaching even if its not useful that turn?
Unless your stealthy but then your default would not be defend anyway.
The benefit is that when you sweep for commanders without orders, using the 'n' key, the preachers who have maxed out a province will be highlighted. Then you automatically know they are ready to be moved, or used in some other way, other than sitting there doing absolutely nothing. :P