We used to shoot the Cabelas catalog with ISO 25 Megavision 3 Pass LF Backs!! They were not more or less efficient, they were just different tools for different uses. It all depends what systems you are talking about. You want to make a blanket statement about ALL digital systems.
Well, if we're talking about an exposure without a literal neutral density filter, and a
single exposure, with current technology, then really, what a low minimum ISO
is (assuming that it does not have compromised headroom) is the camera failing to capture photons striking its surface. It is not a quality feature, except that on the same camera, relative to the higher ISOs, you capture more photons. A camera with a lower minimum ISO does not have less noise than one with a higher minimum ISO; AOTBE, they have the same noise at their lowest ISO, whatever it is, and the one with the higher minimum ISO has less noise at the same ISOs, where the ISOs overlap.
A pixel that captures X number of photons at a certain level of illumination, and has Y read noise, in electrons, has the same DR, same noise, as any other pixel with X and Y, regardless of the ISO.
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You can save electricity with a more sensitive camera, though.