Your citation is about using GPS as reference for electrical grid operations/control purposes (very common if your use case can rely on GPS versus local high precision time sources such as a cesium clock). If you were referring to using electrical grid frequency for time keeping, that is a suboptimal solution due to frequency stability nuance.
https://www.nist.gov/publications/time-and-frequency-electri... ("Due to the efforts of Henry Warren, inventor of the Telechron electric clock, electric power companies have been a source of time and frequency reference for the public for over a hundred years. However, advances in technology and changes in the electric power industry have generated a movement within the industry to end the time-reference service.")