size, weight & cost
This is where you might expect Nikon’s DX cameras to have an advantage, and they do at the beginners’ end of the market. But once you start looking at more advanced models the differences quickly disappear. Indeed, the D500’s body is slightly larger than the D750’s, not smaller. It’s true that DX lenses are generally smaller than their FX counterparts and less expensive, but that’s partly because there is a dearth of pro-quality constant-aperture zooms at shorter focal lengths for the DX format. Variable-aperture lenses are lighter and cheaper partly due to their lower spec.
You might assume that an FX-format Nikon system would be bigger, heavier and more expensive, but there’s more going on than just an increase in size. In fact, the range of lenses available for the DX and FX formats is not directly equivalent. Direct lens comparisons are difficult because most DX-format lenses are designed for cost-conscious consumers, while most FX-format lenses are designed for quality-conscious pros. Our tables compare like-for-like lenses as closely as we can get them, but there are important differences in the three key lens areas we’ve chosen. What it boils down to is that DX gives you the value, but FX gives you the choice. Currently, Nikon’s lens development seems heavily focused (sorry) on the FX format rather than DX
If you try to match lens specs across both formats, the costs work out closer than you might expect