They could help avoid judicial conflicts of interest.
For justice to be blind, the nine justices of the US Supreme Court need to have blind trusts.
An embarrassing situation arose in May when the high court affirmed a US Court of Appeals ruling permitting a landmark $400 billion lawsuit, American Isuzu Motors v. Ntsebeza, to proceed because four Supreme Court justices had conflicts of interest involving the plaintiff companies and had to recuse themselves from the case.
The result was a setback to dozens of multinational corporations being sued in federal court for allegedly aiding and abetting South Africa's apartheid regime because they did business there when its abhorrent system of racial segregation was in place.
If the suit eventually prevails, it could threaten America's currently fragile economy by opening the door to lawsuits against other US firms that operated in countries whose rulers imposed unjust sanctions against their citizens.
The US, British, German, Swiss, and South African governments had urged the Supreme Court to accept the case and overturn the lower court's ruling.
South Africa feared that a victory by the plaintiffs' lawyers would dry up desperately needed foreign investment and hurt the ongoing effort for racial reconciliation.