It's market size. It shows the interest in some activity. Laundry and airfare are for sure necessary & valuable activities, whereas the interest of betting (for a society) is questionable.
The question is what do you do with your money. If you are a pharaon, and pay a good salary to build pyramids, is that good? People get paid, pharaon gets his pyramid. However, as a society, the loss is all the efforts that could have been spent on something much more useful, like hospitals, schools, roads... For the betting industry, no money is lost, it goes to the winner or the house. But how will these people use their money next?
