if working correctly for you w/no apparent issues then dont reset, your option.
if having issues and cant reslove them then reset for troubleshooting .
dev will usually not offer support until u do a reset.
some fw updates require a reset depending on the code/packages being updated and dev will usually state this.
This is what Merlin wrote in post #1 of this topic:
"A factory default reset is required specifically for the RT-AC68U, due to the switch to a new SDK + wireless driver. Some people reported having issues with the 2.4 GHz band with this new SDK- if that's your case, the only solution at this time is to revert "