Some need a little moisture, while others can survive months without. Probably all would be happy with a little moisture, but some would rot if too wet. I'd be surprised if any need to be completely dry as a rock, although being able to survive with almost no moisture in the air and pot is a good survival skill if living with me:
The speck of green is a desperate scream for some water.
That's a 2 1/2" square pot's worth of peat mix. Rock solid. Rehydrating peat that's so dry takes some effort: pouring water over it won't work; a wick won't work; warm water poured/sprayed/drizzled onto it won't work; warm water in a saucer will only moisten part of it; and sitting it in a deep bowl of warm water doesn't guarantee that it will moisten throughout. I once put a 4" pot of similarly dry peat mix in warm water for a day: although half was soaking wet, the other half of it was 100% dry. (And anecdotally: that was a Saintpaulia that had been without water for months - those are some succulent leaves....)
Back to the topic: some Sinningia tubers will shrivel and disappear if left without water for too long. The dryness/humidity of the air makes a difference too: a tuber that would be fine without watering in a greenhouse may not survive in a dry heated room. A good rule of thumb is to not let any tuber get this dry: even if they say to withhold water while dormant.