Chances are that unless you're playing Deadlands, opportunities to use that skill never come up.
In Wiseguys, America's gambling capital; Las Vegas is front and center. The temptation to test your luck and beat the house is everywhere. However, it isn't all you can do with the Gambling skill.
Want to run your own casino or bookmaking business? That's Gambling. You can look at it as a knowledge skill. You know how to set the odds of a wager, how comping works, and what measures are set in place to stop cheating and how to defeat them. Which casino has the best winning odds in town?
In most cases, this would be a use of Common Knowledge but when it involves gambling, the Gambling skill is a valid choice.
Is that gambler over there cheating? Where is the accomplice? Which scam are they working on? Notice can definitely be used in those circumstances but Gambling is also a perfect fit.