Usually in my game I would rest after fights, not before them. So, if I did a fight, even if it was small, and I didn't feel like my party could handle another something I would just rest then and there. The only time I experienced something in the world-changing after I had rested was
in Act I. I went in the cave and didn't want to kill it myself, so I rested and when I came back out of rest it was dead. But, take that with a grain of salt because I really don't know how many instances like that there are. I would just recommend switching around when you rest.
