An update should be built on the idea that it's updating a previous version. If we had to do a factory reset for every computer update, Wednesday wouldn't be "hump day", it would be "back to pencil and paper day".
If you reset before the update, the only reason to reset after the update is that the update is defective.
Totally different thing - that resets the hardware. If there's garbage in the cache it'll still be there after a power cycle. But if the wifi radio is hung, it'll clear with a power cycle. (The only relationship is if there's garbage in RAM - and that will clear on a plain old power key menu reset.)