How does having an offshore bank account help? From my (limited) understanding, the US taxes on all income worldwide, so placing money offshore would still be taxed normally. Why, then, do high net worth individuals open offshore bank accounts (ex. Panama Papers, etc)?

How does having an offshore bank account help? From my (limited) understanding, the U.S. taxes on all income worldwide, so placing money offshore would still be taxed normally. 

Why, then, do high net worth individuals open offshore bank accounts (ex. Panama Papers, etc)?