I like getting focus just right, such as on the iris of the eye.
So this pinpoint AF feature sounds great:
Achieve precise focus on a very small area
Pinpoint AF The D850’s new pinpoint AF mode is a valuable asset for macro shooting in live view photography. It uses a focus area that’s a quarter the size of conventional normal-area AF, enabling you to achieve precise focus on small details — particularly useful when focusing on subjects such as the pistil or stamen of a flower.
The focus peaking if implemented well *might* be useful, which would be a first for me—never have I found a camera in which focus peaking did more than get me pretty close, which is pretty bad.
Accurate manual focus confirmation
Focus peaking display Many landscape photographers prefer to use manual focus for macro shots, such as when shooting at wide apertures like f/1.4 or f/2.8 with a shallow depth of field. The D850’s focus peaking display makes it easier to confirm manual focus during live view, including when zooming. The camera detects the scene’s highest-contrast edges — meaning they are in focus — and highlights them in a designated color. You can choose to display highlights in red, white, yellow or blue, according to your subject’s own coloration, and adjust between three levels of detection sensitivity.
I assume that Nikon is improving upon the awful “green dot” focus confirmation in speaking to “more accuracy in manual focus”. It remains to be seen if this works accurately enough to be useful. The green dot thing was useless, far too inaccurate with results that would vary widely depending on focusing near-to-far or far-to-near, pretty much a junk feature. Maybe this new implementation will be useful in some circumstances.
More accuracy in manual focus
Electronic rangefinder with improved precision In addition to offering superb autofocus performance, the D850 also makes manual focusing more precise. Its electronic rangefinder identifies whether a subject is in focus more accurately than ever before, allowing you to capture sharp images when focusing in manual mode, or using a manual focus lens.
How much more accurately? I’d want to see 4X or so.