What does obtaining clearance from ATC before entering a controlled taxiway ensure?

Obtaining clearance from Air Traffic Control (ATC) before entering a controlled taxiway is crucial as it ensures adherence to safety protocols. ATC is responsible for managing the movement of aircraft and vehicles on the airfield, and by requiring clearance, they help maintain an organized and safe environment. This process minimizes the risk of accidents, such as collisions between aircraft and vehicles, by ensuring that all parties are aware of each other's movements and intentions.

While other factors, such as cost-effectiveness, timeliness, and unrestricted access, might play a role in operational logistics, they do not directly address the primary concern of safety. The key focus in airside operations is to prioritize safety to protect lives, equipment, and the overall operation of the airport. Therefore, obtaining that clearance serves as an essential safety measure.