Social sharing and refer-a-friend techniques are one of the tried and true growth hacking ideas, but Groupon has a twist on it.
It worked on the principle that you need enough people to take a deal to GET the deal, so if you don’t share, then everyone potentially misses out, because the deal will expire. It’s a great use of FOMO and urgency in marketing.
If you do share, you get the deal, and Groupon gets new users that it can market new deals to. Sweet, right?