Not "required". You can delete it at any time, and/or ignore it by not having an M501 in config.g, or by executing an M502. Specifically:
M500 writes a subset of currently active settings to /sys/config-override.g. (Want to know which subset? Do an M500 and look in /sys/config-override.g).
M501 reads from /sys/config-override.g and executes the commands found there. Assuming they were written with an M500, this has the net effect of setting parameters to what was 'saved' with the M500.
M502 reads that same subset from /sys/config.g, effectively 'undoing' anything that was done with an M500/M501.
Those three commands are it... Therefore, if you want /sys/config-override.g to have any effect at printer boot, there MUST be an M501 in /sys/config.g, Preferably near the end. If you want to have it ignored, just don't have an M501 in /sys/config.g.