Utility boxes are critical in which of the following scenarios?

Utility boxes play a crucial role in facilitating service connections, which involves the connection of electrical service from the utility supply to the building's electrical system. These boxes are designed to provide a safe, enclosed space where power can enter a structure, allowing for the distribution of electricity throughout the building.

When it comes to service connections, utility boxes must be robust and compliant with the National Electrical Code to handle the high voltages and currents involved. They protect the wiring and connections from environmental factors, help prevent accidental contact with live wires, and ensure that safety standards are met.

While the other choices involve important aspects of electrical wiring, they do not emphasize the primary function of utility boxes as directly as facilitating service connections does. Joining wires in fixtures, connecting power to switches, and housing receptacles are typically managed by other types of boxes or enclosures more specific to those tasks. Utility boxes specifically serve the broader, crucial role in managing incoming service connections, which underscores their importance in the electrical infrastructure of a building.