On the D850 touch screen is great for navigating menus and it can be useed to change focus points when in live view mode. I wonder if "touchpad" focus could be added in a firmware update.
^^ 't would be nice!
I can see how it would be helpful for someone who does a lot of people photography, like Terri. With one touch you can put the focus point on the eyes. But I don't photograph people very much and after trying it on my D5500 I don't find it very helpful. I think I'll stick to back-button focus.
My wife tried it on her D5500 and found that her nose touches the screen and changes the focus point.
YMMV as they say.