What a clock like this is good for is calibrating scientific equipment, measuring the speed of atomic particles, possibly the expansion of the universe, Doppler effect etc.
I was trying to be humorous. But I differ with you about a second. A 60th of a minute, and a minute is a 60th of an hour, the hour being a 24th of a day in which the Earth rotates once relative to the Sun’s position. So if the rotation of the Earth speeds up, so does a second. Minutely. Earthquakes, tides and wind all constantly alter the Earth’s rotational speed, but only in microseconds. Over long periods of time, it adds up but only as milliseconds. But a second can alter in duration.