From the site:
"We use cash prizes to make weight loss and fitness more fun and effective! Our famous HealthyWager lets you make a personalized bet on your own weight loss – prizes up to $10,000. "
Of course the more you wager and need to lose the more you’ll win. But if you don’t make your weight you don’t win the cash. Seems like a good way to make some extra money if you’re already motivated or going on s cutting phase.