there's more encounters as well with world level increase but you can dial it back if you encounter the preacher and pay him 10000 tp+1000 (since it rounds down by 1 difficulty level if you don't) but otherwise major changes seem to happen every 25-35 world difficulty levels minor ones every 5 like for the eastern cave there will be no fat orc in the goblin cave for the rescue mission for the merchants daughter but at level 5 there is one in there instead of a goblin and at 25 or 35 not sure which it becomes very crowded in that cave