Is an artificial external source of light required even with a low-noise high ISO range?

Question

Is an artificial external source of light required even if you have a camera with a high range of effectively noiseless ISO?

Are there some special cases which "need" external lights, at all costs?

Answer

Lighting is about a lot more than simply making a subject visible to the camera, it can change a shot dramatically so always relying on naturally occurring light severely limits creative outcome. You have to bear in mind that high ISO shots rely on the available light and will simply make the scene uniformly brighter the higher you go. The available light may be perfectly adequate to get a correct exposure at high ISO but may be so even for instance that the resulting image is flat and boring. In the other extreme if available light is very low boosting ISO will just give a uniformly bright image with no tonal range. Introducing external lights will add contrast and depth to the shot if done carefully.

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