I used to always set ISO for each shot, now it is a mix. It partly depends what lens I am using. Also the auto ISO on my old D90 is not as good as newer cameras, e.g. I can't have a variable shutter speed dependent on focal length.
When I am using my 300mm f/4 for wildlife I just set the lens wide open and have auto ISO on with a shutter speed of 1/500th and I just concentrate on getting the shot.
When i shoot landscape the camera is on a tripod and I am at base ISO.
im finding the more i can put on auto for where i need to be very quick the better.
just cant be faffing about with settings and miss the shot completely