In the United States, Generally Accepted Accounting Principles (GAAP) are required to be used by public companies so that users of the financial statements can properly interpret results. It makes sense to have a set of rules common to all businesses, such that financial statement users can know what various line items and metrics mean.
If companies were allowed to make up their own accounting rules and measures, no one would know what the numbers really mean. And that is precisely what Groupon (GRPN) is hoping will happen when would-be investors look at the company’s numbers.