On most engines seeing rpms under 6500, it's cost effective to just run what the factory did.
What a lot of race engine builders do, and how it's trickled down to the street, has been distorted over the last 45 years. Sure, a properly balanced engine runs smoother, and that's the first clue - owner comfort. Driving a buzz box doesn't connote quality. It's why some four cylinders are fitted with balancer shafts to reduce the vibration. BUT - those smoothly running motors are no guarantee of vastly improved longevity. They wear out just the same; some, like the 2.5 Chrysler, don't even last that long. (Sure, ask me how I know.)
There's another thing going on in the crankcase most don't know about. All the
oil slinging around isn't formulated to be that slick, it has a tendency to cling. What good is it if it runs off immediately? It needs to stay there and keep doing it's job, providing a place for metal to spin separated from the other metals.
Smokey Yunick took photos of that back in the '60's - it's in his book Power Secrets, and it shows a crank at speed with about two quarts of
oil wrapped around it in a disgusting blob. And - it wasn't smoothed out, it has heavy places that move around.
How can your crank be balanced with over 16 oz of
oil floating around on it knocking it out of balance? ITS NOT BALANCED. And that's why the harmonic balancer is there to smooth out all those randomly occurring vibrations.
Go look up racing pans and windage trays, what's the one thing many race cars use? Crank scrapers and strippers, fitted within thousandths of an inch to clean off all that oil and 1) return it to the oil pickup, 2) reduce the rotational inertia. Look around some more and you'll see vendors selling coatings for the crank throws and rods that help sling off oil that sticks to them.
Guys, we've been getting sold high precision balancing jobs for over 40 years, but when you get to actually talk to a machinist in a shop building his own, he puts it together with the factory balance - and tolerance, which is good enough for any stock crank.
It's just another high speed low drag things that consume cubic dollars in an otherwise warmed over stock rebuild, and a lot the myth about it is overblown. If you're not running a crank scraper, your engine simply will not ever be completely balanced while running, and the money was wasted.