higher ISO when low light/moving subjects/potential camera movement with the lens already wide open conspire to prevent using lower ISO and getting proper exposure.
Given the same amount of exposure, sometimes you may prefer smaller or bigger aperture because you may want high or low depth of field.
Similarly, sometimes you may prefer slow or fast shutter speed, because you may want to freeze the action or you may want the blurred effect.
In case of ISO, is there ever a reason to prefer high ISO to low ISO , all other things being equal? (By all other things being equal, I mean exposure is the same i.e. image is properly exposed. Obviously changing the ISO means you will have to change the other 2 parameters to ensure same exposure.)
To clarify some confusion about what I mean, I will try to give a concrete example.
Let us say, you have 5 images of a well lit subject, shot with different apertures, all properly exposed (through adjusting the other 2 parameters). I can understand that one may choose the lowest aperture or the highest aperture image based on what kind of DOF he wants.
Similarly, if I have five properly exposed images with different shutter speeds, one can choose any of them based on whether they want blurry effect or freeze framed photo.
So, if I have five properly exposed images with different ISO settings, is there any reason one would not go for lowest one (apart from just the artistic/stylistic choice of someone who prefers higher noise in the image)?
My restrictions are deliberately designed to eliminate the situation where you need sufficient exposure and therefore HAVE to use high ISO. That is not what I am asking. I know, in those cases, you HAVE to use high ISO. I am asking about the cases where you do not HAVE to use high ISO.
Also, I found one other great answer by Matt Grum on this site which helped my understanding a lot. Thank you Saaru Lindestøkke for pointing me to that.
What is “ISO” on a digital camera?
The answer is in some places quite contrary to what is the common understanding about ISO settings, but if it is true (and from the huge upvotes in that answer, I assume it is true), then that is a very helpful answer.