A man may think of gambling as his entertainment when he feels bored at work. Here the gambler will find at least some human solace but it is expected to be a personal matter but indirectly contribute to the society to some extent. However, we know directly about some things such as when a casino is opened, employment will be created there, government institutions will get tax and various types of business can be created around that casino. These are directly related to the development of the society. There are many places in the world that people know only for the casino. So I think gambling has immense importance socially as well.
Usually the reason why gambling is legalized is not because the government thinks they are opening a goldmine and will make so much money. The reason is that if they don't legalize it, the black market for gambling opportunities will explode and spread like wildfire especially on the Internet. That's why some states legalize it and raise a certain amount of tax on the activities or winnings and profits made by the casino if they are registered correctly.
Really no government (maybe except for Las Vegas) thinks about casinos as valuable employers. The tax money that casinos pay is used to cure the problems that casinos create. It doesn't contribute to society in a net positive way.