Restaurant and business reviews exist so that customers can accurately rate their experiences, to help other people decide where they should, and should not, spend their money. Unfortunately, way too many people abuse the system, and leave bad reviews complaining for dumb or petty reasons that have nothing to do with the quality of the service they received. Or they intentionally leave out pertinent details that would cast their experience in an entirely different light.
There's no way to gauge the exact cost a small business can incur when a disgruntled customer chooses to smear them in a bad review. But seeing the customer get publicly called out on their bullsh*t? Priceless.