Most of the time customer usage is fairly predictable. Refrigerators, for example, are always on, and use about 14 percent of domestic power. Freezers use another 4 percent. Based on this data, the utility can bank on needing to make and transport a certain baseline of power all the time. This is one of the advantages of nuclear power plants. They may be difficult to ramp up or down quickly, but since they provide 20 percent of American power with exceptional reliability, they are basically big machines for transforming plutonium into refrigeration.
