A defining difference between service and manufacturing is the inability of a service organization to inventory the act of service. If the demands at New York's George Washington Bridge or the San Francisco Bay Bridge were constant over the course of a day, there would be a need for only one deck. However, commuters cannot be inventoried like air conditioners. Second decks and additional toll-takers are needed to handle peak traffic. Responding to peaks in a service business requires additional capacity in some form.
Peaks can also be seasonal.
Tax preparation, crop harvesting and holiday travel are obvious examples. Migrant workers historically have satisfied farm requirements. Companies providing holiday travel try to level demand by price mechanisms but, unfortunately this is a far from perfect solution. Going to grandma's for Thanksgiving is close to immutable. Hiring someone for a full day when only half a day of work is required raises costs substantially and contributes to inflation.