Mesh Leveling Questions

I upgraded to Marlin RC8 and did a manual Mesh Level process as instructed here: [marlinfw.org]
And saved it to EEPROM with M500.

Questions are: Anything else? Anything else needs to be done to 'enable' the mesh for leveling the bed? Does it automagically go into effect every time I turn the printer on, or is there a gcode command I need to set in my print start script?

The reason I ask, is I don't see the z-axis motor turning on the first layer as its printing. And the LCD panel Z position never changes either.

Also: the Configuration.h file has an entry: ENABLE_LEVELING_FADE_HEIGHT which I #defined, and it says the Height can be set with the M420 Z command. That command variation is not documented in the RepRap g-code Wiki: [reprap.org]
Plus is does not say if this needs to be done every time the printer is turned on, or a print is started, or what the default value is....Any ideas?

Thanks!

BTW, here is my mesh results:

Recv: Mesh bed leveling:
Recv: echo:  M420 S1 X4 Y4
Recv: echo:  G29 S3 X1 Y1 Z4.07500
Recv: echo:  G29 S3 X2 Y1 Z4.07500
Recv: echo:  G29 S3 X3 Y1 Z4.07500
Recv: echo:  G29 S3 X4 Y1 Z4.07500
Recv: echo:  G29 S3 X1 Y2 Z4.07500
Recv: echo:  G29 S3 X2 Y2 Z4.10000
Recv: echo:  G29 S3 X3 Y2 Z4.10000
Recv: echo:  G29 S3 X4 Y2 Z4.10000
Recv: echo:  G29 S3 X1 Y3 Z4.07500
Recv: echo:  G29 S3 X2 Y3 Z4.10000
Recv: echo:  G29 S3 X3 Y3 Z4.10000
Recv: echo:  G29 S3 X4 Y3 Z4.07500
Recv: echo:  G29 S3 X1 Y4 Z4.05000
Recv: echo:  G29 S3 X2 Y4 Z4.07500
Recv: echo:  G29 S3 X3 Y4 Z4.07500
Recv: echo:  G29 S3 X4 Y4 Z4.05000