I sometimes use Auto ISO in Aperture Priority when I am moving quickly through different lighting situations, from an open square then down a darker alley for example. On my older camera I could set the minimum shutter speed and the maximum ISO. Normally the minimum shutter speed was a reciprocal of the longest end of the zoom lens I had, so for my 16-85mm lens I set it to 1/90th sec. My new camera also takes into account the focal length when setting the Auto ISO, so whereas the shutter speed at 16mm would have been 1/90 sec, the camera would now set between 1/15th and 1/20th sec. That could result in the camera setting the ISO about 2 Stops less that it would have before, so less noise.
The Auto ISO can also be set to go a bit faster than the reciprocal of the focal length, if I am having a shaky day.

Add that to the newer camera being a lot better in low light than the previous camera, and I am a lot more confident with Auto ISO. On my previous camera the maximum ISO I was comfortable using was 800-1600, on the new camera I get less noise at ISO 6400, and I could even go a touch higher if needed.
Also, sometimes when I am doing sport pics in Manual Mode, Cricket for example, when I am in a static location and the background doesn't change, and I want a certain Aperture and Shutter Speed combination, I set the camera to Auto ISO to take into account any changing light levels.
Most new cameras are so good with higher ISO that for most every day photography higher ISO levels are less of a problem, but you should always do a bit of testing to see what levels you are personally happy to go up to.
