In reality I rest every time I hear a NPC say that they're tired, because that indicates there is a camp cutscene. This means I rest WAY too often for my tastes, like after every area and every other combat. In my most recent run, prior to getting to the grove, I rested:
-after landing on the beach, because I knew there would be a "Tav alone" scene
-after meeting Gale and Astarion
-after cleaning out the crypts
-possibly one more time, I don't exactly remember, likely after rescuing Lae'zel (this might have happened before the crypts)
At least 2 of the above were directly in response to NPC Companion voice barks. Midway through this playthrough I lost all interest continuing to play (for numerous reasons, but at least partly) because I didn't want to miss camp cutscenes, but LR'ing this often ruined any hint of game difficulty = interest in combat. We shouldn't have to choose between the two.
I would strongly prefer to be conservative with my resources and only rest when I'm low on them and don't think I can get through another fight, which would probably match with the ~6-8 LRs mentioned by other posters. That's what I did on my first playthrough before I realized how much content I was missing by doing so.
- Compared to the above, in my first playthrough, I didn't rest until after encountering Nettie.
