I found a good use for DX mode, which crops the sensor to the DX size, which is 43% of the full-frame area.
For focus shift tests, I need only the central area, the rest of the frame is throw-away useless.
For such cases, DX mode is perfect; it cuts the file sizes down from ~ 48MB to ~20MB, saving more than half the storage. Too bad the Nikon viewfinder can’t optically zoom somehow. There are other crop mode choices, such as 5:4, etc.
Note also that file size for the same scene across apertures is an excellent measure of the total detail recorded, which includes the effects of depth of field, diffraction, and lens performance.
By this metric, we can se that f/8 provides the peak level of detail.
Of course, f/2.8 might prove far more attractive than f/16 given its much higher micro contrast than f/16 (with a good lens). But f/16 has much greater depth of field, with a sacrifice to micro contrast.