It depends on the camera model how well they use the Auto ISO setting. Some cameras offer no control over just turning it on, and then you are left with what the programmers set as to how the camera reacts to the changing light whilst changing the ISO setting,normally raising the ISO if the camera's shutter speed were to fall below 1/60th second in low light conditions. I had a Canon compact which would bump the ISO up to thousands when all that was needed was a few hundred increase.
I have an older Nikon DSLR which allowed you to set the base ISO, and the highest ISO I wanted it to go up to, and that worked pretty well, though sometimes slightly higher than necessary, when using a wide angle lens for example. A lot of Auto ISO function take 1/60th second as a safe hand holding shutter speed, which would be OK if we all only used 50mm lenses.
I found that if I had say a 16mm lens on, it raised the ISO 1-3 stops more than it needed to to get the 1/60th second, when I could probably hand held about 1/20th second. 1/60th of a second is also not fast enough if you are using a 300mm lens even if the camera thinks it is.
My current Nikon DSLR in Auto ISO takes into account the focal length of the lens when altering the ISO, so as to give a shutter speed that is a reciprocal of the focal length, so on a 50mm lens for example, it wouldn't raise the ISO until the shutter would fall below 1/50th in the lighting conditions. If the lens is at 16mm, it wouldn't raise the ISO until it measured the shutter falling below about 1/20th second, and about 1/300th second at 300mm. You can bias the setting slightly whether you are steadier or shakier hand holder.
Add to that most of my lenses have image stabilisation, (2 out of 3) and Aperture Priority, IS and Auto ISO work amazingly well 95% of the time, and the occasions when I get blurry images is when I haven't been observant of the shutter speed had haven't been totally concentrating on my hand holding technique. My images are less noisy than my previous camera because of the sensor improvements, (it was 8 years between cameras, so a huge improvement in the ISO performance) but also because it is not raising the ISO more than it needs to at lower focal lengths.
I think a lot of current mid-high level cameras may implement ISO in this way.
It goes with out saying that if the camera is on a solid platform, and nothing in the scene needs to be frozen by a fast shutter speed, the Auto ISO is off, as is the image stabilisation, the camera is at its lowest ISO, and the cameras takes as longs as it thinks it needs.