Groupon's modus operandi is that the business is (usually) making a loss or zero/negligible profit from the deal for the opportunity to generate future (post-groupon) business from those customers (or their friends).

Spending no money at all might either be worse (they've lost more than they earned) or no better (zero sum) than buying the coupon depending on your future intentions.

Or do you mean that you've returned and purchased again from those places?