Tiny instabilities in those orbiting clocks contribute at least a few meters of error to single-receiver GPS measurements. Making the clocks smaller (so that more of them can fit on each satellite) and increasing their stability could reduce such errors to fractions of a meter. Pilots landing on narrow airstrips at night would appreciate the improvement. So would surveyors, prospectors, search and rescue teams ... and farmers. 'Precision farmers' already use GPS-guided tractors to dispense custom-doses of water, fertilizer and pesticides over garden-sized plots. Better GPS data could guide those tractors to individual rows or perhaps even to individual plants for special care.
'Watch the stars, and from them learn.
To the Master's honor all must turn,
Each in its track, without sound,
Forever tracing Newton's ground.'