Gamblers require measures of control, measures that are extra important when these gamblers are playing at tables that don't use or need skill, like the Roulette table. This is why a bankroll is made. Even if a gambler doesn't have controls beyond the existence of a bankroll, it can do wonders to make sure that a gambler doesn't end up throwing away their immediate monetary future. Of course, there's much more to a gambler's bankroll than simply having one. Bankroll management could potentially be a life saving skill for those with less than optimal self control but want to play at the casinos anyway.
Gambling is inherently about putting things on the line. Whenever a person gambles, they're essentially putting their money on the future - it sounds epic, but it can get very gritty, very fast. Predicting the way the roll of the dice will affect your bankroll has been a science long due. In effect, no matter what a gambler does, if a certain amount of luck isn't with them they won't fail. That's why bankroll management is there. It carries a lot of the weight that the gambler's skill cannot.
Putting limitations on the amount of money you can pull out of your bankroll in any given day is a good step in terms of bankroll management. A person could state a long list of reasons why people put limits, but for the most part, it boils down to people being people. People can't help being people and people of course, get angry. Poker and its psychological variant, Texas Hold'em, are games that are particularly fond of making people angry. From a long stream of bad hands and cards in general to the river card beating what was originally a good bet, poker can make a person angry for a variety of reasons. It can get alarmingly tempting to just sit at a Texas Hold'em table, abusing your bankroll until you end up spending far more than you would have wanted to in the morning.
That's with a game that lets you offset luck with skill - what more with games like roulette and slots, who really don't care for what you do? Limitations are important in any endeavor and that importance can only be highlighted in gambling. Gambling is supposed to be entertaining and is only at certain times profitable. Take careful note of that, manage your bankroll well and perhaps, you can avoid any excessive losses emotionally and monetarily.