The important thing should be if they are actually playing with the amount they can afford to lose than an amount which is potentially high above their expectations with this, there could be no fun while gambling. The only difference between millionaire as you said is just that they wouldn't that affected because they have sufficiently enough than those who are trying to make gambling a source of livelihood.
Without a doubt it is a great way of seeing things, because if we start from the fact that when we are looking to win in a casino it is because we must measure ourselves with our money , rich people have many ways to earn money, there are some who dream of spending time winning , if that were the case for everyone I think that casinos would have less profits than they do now, since rich people only think about investing to Multiply their money and not having fun to Spend time in a different way.
Indeed, the point of spending spare and not to overexceed will allow gamblers to limit their losses and prevent casinos to earned a lot though not the thing that's happening nowadays since most gamblers don't have any limitations in terms of spending money, most thinks that if luck permit they'll be able to win more and enjoy the privilege but at the end it's the casino that win a lot and enjoy the benefits.