I think the reason for recommending that is just to ensure you have no system overclocks applied that could cause the system to hang while flashing(this would be bad). I have NEVER reset it to update a bios and been good so far(but it will not hurt to do it, you have to reset after doing that for the new settings to take as well).
As said above, you will get defaults after a flash most times anyway. It is a good idea to take note of all your settings first. Some can save to a flash drive, but save slots in the bios itself may be overwritten so those do not always work to hold settings while flashing.