Diminishing returns, probably, especially if you live in a location where you're going to be setting your watch twice a year anyway for daylight saving.
My SBGP017 has a jump-hour movement that I can use for DST (or while traveling) to set the hour hand without hacking the seconds hand. That's how I know its accuracy over an entire year, even though I've adjusted it for DST twice since I got it and done some international traveling as well. I'll literally only ever need to set the time once every battery change.
Of course it's diminishing returns regardless, but the accuracy achievable is nevertheless impressive.
