I've been using digital Nikon cameras since the D70 and, for the most part, have been a serious student of the controls. Still, as I became more and more used to the settings, and each camera wasn't that different from the last, I've definitely let the finer points slip, especially if I wasn't using that setting much.
Enter "Auto ISO." I read Steve Perry's excellent book about Nikon autofocus and listened to his video extolling the virtues of auto ISO with manual exposure, but it wan't until Arthur Morris, having plunged into a Nikon setup only recently mentioned the sticky setting of exposure compensation that I decided to look into this combo a bit deeper. I could find nowhere in Nikon's documentation where it was stated what actually happened with Auto ISO and exposure compensation, and no one writing on the web had clearly spelled it out. So, I decided it really isn't that hard to figure it out. All I needed was a few minutes with my own D850 and adjusting the settings while in manual plus auto ISO.
Here's the thing: Auto ISO and manual exposure adjusts the ISO to give a standard histogram, within the limits that it can, based on the upper and lower limits the user sets. If exposure compensation is dialed in, the the ISO is adjusted upward or downward to match that instruction. shutter speed and aperture are as set in the manual settings, but ISO varies not just to maintain a normal histogram, but also to allow for the extra brightness or darkness dialed in by "exposure compensation.
I remain cautious about auto ISO and manual. Certainly it can be useful for rapidly changing light when I really need to keep a minimum shutter speed for moving targets. However, it may negate some interesting light features that manual setting allows me to accentuate. If I add the "exposure compensation," auto becomes even more "auto." I's rare that this is actually contributing to whatever unique quality of light I was seeking.
Granted, this is coming from a photographer torn between landscapes and wildlife. If I ever figure out that I should just stick with one or the other, then perhaps these dilemmas will be resolved. On the other hand, great light is great light, and I may never really want it "compensated."