Calibrating slightly less accurate clocks. What those clocks are used for I have no idea, but there’s times you need a good traceable measurement for some calibration of your own and your uncertainty stack can start to add up. The better, smaller, and cheaper NISTs equipment is the better your local cal lab will be and the easier your work is.

Try finding a thermometer setup that’s better than 1 degree accurate from 0-400C. It might be more than you expect. Now imagine you want to measure some property of a sensor or material as function of temperature using your new thermometer, add in the cost of an oil baths and precision multimeters. Now say you want to create your own golden standard with the best precision you can muster, your expensive oil bath is looking lacking and you’re buying Vienna mean standard ocean water...