That rule has been in effect for a very long time. Guys do it but in my opinion it doesn't really help. Most people when they throw a bad shot "mis hit" the ball. So, on top of a slight miss at the bottom, you accentuate the lack of downlane motion because the ball doesn't flare as much and find the sanded part of the flares.

The result ends up being a washout instead of a soft 10 pin. But if you would rather try to cheat go ahead. Been happening since bowling was invented.

The coverstock can only have one finish all the way around. The Quantum Helix had a pearl urethane stripe surrounded by a solid, but it was all sanded the same.

You could say the same thing anout static weights, there's probably a lot of rules that are or should be extinct.

Of all the rules the USBC wants to uphold. The most amusing part of it is... there is no way proving someone doing this other than seeing them do it.

Is there any harm in doing this to a ball?
Is there any harm to the lanes by doing this?

With all the cores and coverstocks we have available to us today this rule seems kind of past its time.