What Groupon primarily attracts is cheapskates. People who are only interested in the lowest price and then move on. Belligerent assholes who come into your business with an coupon they know has expired and then scream at you for not honoring it. This is well documented by the many businesses who have lost money on the Groupon scam.
That may be one kind of customer but my wife and I used Groupon to have new experiences we otherwise never would have tried.
For example, we used Groupons to get an archery lesson, to take a massage class, to stay in a Victorian mansion turned B&B, and to take guided kayak tour of a local slough.
The businesses *might* have made money on us (I have no idea about their cost structures) but without Groupon they never would have seen us as customers because a full-price archery lesson (for example) wouldn't have attracted us as customers.
I think service business might make money on Groupon, I don't know. It seems a few services and "experience" businesses are always on Groupon.