[time-nuts] As there a hobby application of precise time or frequency measurement except for being a time nut?

[Erik Kaashoek]

Maybe the subject line is a bit clickbait but this is a serious question.
Hobby VNA are used to measure impedance for antenna, amplifiers, 
filters, PCB's and cables. Many applications for a VNA outside the 
professional world.
Hobby spectrum analyzers are user for hunting RFI, measuring harmonics 
of active devices, assessing what part of the spectrum is still 
available for wireless devices, etc... Again many applications.
But for time and frequency measurement the situation seems to be 
different. What are hobby applications for accurate assessment of 
stability, time or frequency?
For radio amateurs that operate in the GHz bands the accurate assessment 
of the frequencies of their generators is such an application but what 
other applications do exist and what are their requirements regarding 
accuracy?
I'm purposely excluding the applications where the accuracy is the goal 
instead of some usage for accuracy.
Any input is welcome.
Erik.