EMV takes the reach and engagement a piece of earned content produced, and prices it as though it had been bought. It exists to make organic work legible to people who budget in advertising terms.
It is an estimate, and an imperfect one. The choice of comparison rate drives the answer, and earned reach is not interchangeable with paid reach — audiences respond differently to content they were recommended than to content they were served.
Used honestly, EMV is a directional indicator of whether an organic program is producing meaningful reach. Used dishonestly, it is a way to inflate a report.