Sometimes El Nino and La Nina impacts can lead to benefits in parts of the US.  A common example is that heating bills tend to be lower with El Nino in the northern contiguous U.S. b/c El Ninos are often associated with above-average winter temperatures. This is why we we convey El Nino and La Nina "Advisories."  If it meant bad impacts for everyone then we would probably use another word like "La Nina Warning."