- Resting in dungeons
It's impossible to rest in the Zhentarim hide-out, suggesting that they are experimenting with allowed areas for resting.
- Rests before worm take-over
The current build has no limit to the number of rests before the worm takes over, but the story suggests that excessive resting could result in a game loss.
You also can't rest in dungeon under Teahouse. I already wrote about this in some thread, hmm... I think people here just mean by "dungeon" absolutely any area with some enemy. And Larian forbids rest only in DUNGEONS, not in open locations.