Wiki on credit agency uses:-
Credit ratings are used by investors, issuers, investment banks, broker-dealers, and governments. For investors, credit rating agencies increase the range of investment alternatives and provide independent, easy-to-use measurements of relative credit risk; this generally increases the efficiency of the market, lowering costs for both borrowers and lenders. This in turn increases the total supply of risk capital in the economy, leading to stronger growth. It also opens the capital markets to categories of borrower who might otherwise be shut out altogether: small governments, startup companies, hospitals, and universities.
They don’t always get it right Marcos just as any large institution makes mistakes from time to time. However that in no way reduces their use because what else would take their place, Chinese whispers?