"It doesn't matter becuase it could not be more irrelevant. The Supreme Court is not a place where you put certain percentages of certain groups. "
Oh.
There has been some historical reason for geographic balance. As the nation grew, seats were added to the Supreme Court, as the new justice would be in charge of that circuit. Let's see...it went from 6 to 7 in the early 1800's, after Kentucky, Tennessee, and Ohio were added to the union. It went to 9 in what, the 1830's? after a number of other states were added. In the 1860's, after California was added, the Supreme Court was enlarged to 10 justices. The Senate refused to fill any vacancies for Andrew Johnson, and after his term the membership was fixed at 9.
I don't have who is charge of what circuit in front of me, but as I recall, Anthony Kennedy of CA has the AL-FL-GA circuit. I assume lawyers are expected to be familiar with legal issues all around the country today so perhaps the need for geographic balance is gone.
On the other hand, certain senators or blocks thereof may be able to get nominees confirmed, so it may be worth appealing to geography.