I think GP's use of "hand-clocking" to refer to the factthat the z80 can run on a very low clock rate, to the extent that you can have a hand switch that sends individual clock pulses to the processor. This can be useful for testing purposes as well as for low power operation in embedded applications.
As the Z80 doesn't use dynamic registers (I think basically the only "modern" CPU to make this decision) it doesn't need a minimum clock signal speed to refresh the registers as every other CPU does.
This means you can rig up a push button switch and manually advanced the clock one button press at a time.
To me that's super cool. It also makes them really easy to debug.
http://www.thomasloven.com/blog/2013/01/Z80-Tester/