The question is the same, but the answer has changed over the years.
When should you use Auto ISO?
When Darren asked me this question on our last photo tour, the answer I gave was very different than my standard answer when I started leading photo tours in 2009 - 2010.
It's not so much that times have changed but that technology has evolved significantly.
Just five or six years ago, most digital cameras topped out at ISO 1600 - ISO 3200. With that narrow range, noise started to be visible at as low as ISO 800 in many cameras. It was downright distracting by ISO 1600.
When your camera can't be trusted to create clean images north of ISO 1600, you shouldn't leave the ISO decision to chance.
Back then, I counseled that you should change your ISO deliberately, so you can ensure you are always getting the sharpest image possible.
ISO performance in 2015 is incredibly better. It is not uncommon for entry level DSLRs to top out at ISO 128,000. With such a wide range, a DSLR can create noise-free images at much higher DSLR levels. With that increased performance, Auto ISO is not as risky.
Here are a few scenarios when Auto ISO might be helpful.