I really wasn't sure that this was an entire new concept for you'll.
Anyways , I'll explain.
This mainly focuses on the visitors to US. i.e the non US residents who win in gambling or a big jackpot. For example You win $10000 in a gambling . Now the Casino will apply 30% withhold tax , which will leave you back with $7000 as per IRS. So there is a way to get back this 30% without any complications. Only the thing required is the form 1040NR, collect it before leaving the casino. There are many tax refund services who can help you with this.
Yes exactly.... This means retirement is a stage where people want to enjoy. You gamble , you win and you lose a 30 % of the win, it really sounds bad. Hence just a bit emphasizing for the retired people who love gambling .