gaopa wrote:
What about setting it to auto and letting the camera decide?
Fair question, and I can see that it would be a useful setting for some photographers and situations. Here are some things to consider:
1. With the AUTO setting your ISO will be 250 at a minimum, so the lower 125 and 200 values are no longer available to you. If you prefer to use ISO 125 by default, losing that ability is a downside.
2. In some situations we may decide to allow highlights to blow out slightly or shadows to be darker for creative reasons. That choice is no longer yours with the AUTO setting.
You could ameliorate some of this by picking from among he Range Priority settings of AUTO, STRONG, WEAK, but picking one likely means that some scenes would be better with a different setting. (In a sense, once you start considering switching among AUTO and 400% and among AUTO, STRONG, WEAK,and OFF, you can end up needing more manual intervention to manage those choices than would be required if you just used the EC knob and your experience.
I suspect that if you prefer to shoot jpgs rather than raw and prefer not to do post-processing, that using these settings to automatically compensate for challenging situation could be more useful. (I don't shoot jpgs on my Fujifilm camera.)
One more thing to keep in mind. In most real-world photography, exposure is not a precise and absolute thing. If we are honest, in fast moving situations we often don't get a supposedly "perfect" exposure. On average, an automated in-camera process can do better than a photographer who doesn't have a lot of experience dealing with these issues and who prefers to not deal with post processing. On the other hand, a more experienced photographer is more likely to make good choices even in complicated situations, and can even consider their likely post-processing approach as they do.
YMMV.