In the near term, not much. I think Spanner is using GPS synchronized Rubidium clocks, which form an excellent combination. If you want to do much, much better

In the near term, not much. I think Spanner is using GPS synchronized Rubidium clocks, which form an excellent combination. If you want to do much, much better (these new optical clocks are sensitive to the change in gravitational potential of centimeters), you'd need one of these. The primary utility of these clocks in the near term is improved precision physical tests. In the long run, they may form better standards to replace Cesium. Another way to see this is that few, if any, industrial users have their own Cesium or Cesium-competitive optical clocks, which are a factor 1000-ish worse than these new clocks.