Groupon is amazing, and not very cheap marketing that WORKS, unlike a lot of other not very cheap marketing that does not work. And we sold a LOT of Groupons. Some days 80% of customers are Groupons. When you get 2x your normal business walking through the door it's kind of hard not to make money. Cross sales, up sales, post-experience contact, word of mouth... It's not as easy as just setting up a Groupon and watching money roll in, you have to think about it and work hard to turn it into a positive experience.
But then again, this is business, right? Who said it was going to be a safe, easy bet? Groupon is just another way to market your business.
And it happens to be very consistent and effective.