If your device was successfully flashed to 4.1.2, there will be no more OTA/Kies updates to download/install. You can only do a re-download/reinstall if the original update failed and an emergency firmware recovery was required (since the phone will be reverted back to the previous revision before the update).
The reason for doing another hard reset after the install is to remove trace residual files from the initial update/install that may still be present. This primes your device and ensures that most residual files are gone.
Now, doing another hard reset (after all this) depends on the user. I, personally, like to 'flush' my system every 3-6 months to keep it in 'tip-top' shape. Reason is, over time, I can cram too much 'junk' into it and really need to clean it out. Spring cleaning for the phone you might say.
That's why a hard reset never bothers me as others because I am so used to doing them so often.