W-8BEN to open an account

[Sujee]

I am on H1B and my wife is on H4 (No income). Recently, she opened bank account, and banker is asking to sign W-8BEN. What is use of W-8BEN, if there is no income on h4 ?

[JoeF]

There could be income, e.g., from investments. Such income would be taxed at 30% for "non-US persons".