A port has a limited length of quay, and a ship must occupy one continuous stretch of it for the duration of service. Assigning an arriving vessel to the first apparently open place can block another vessel that needs a different length or arrival window.
Each ship enters, berths, receives service, and departs in full view. An initial local choice looks reasonable but leaves a later ship waiting. A revised plan considers the entire set of arrivals before committing quay space. The final comparison weighs the completion of all ships rather than the convenience of one early assignment. Berth allocation is therefore a scheduling problem in both space and time: two ships can overlap only if their hulls do not require the same quay at the same moment. Planning matters because idle water beside a berth is not useful when the remaining contiguous space cannot fit the vessel that is waiting.
An electric train can return energy to the traction system while braking. Another train can use some of it if that train is accelerating at the same time and the electrical connection can carry the power. Without such a match, the opportunity may be lost even though the braking train still produces energy.
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Quay cranes are shared resources. Splitting them evenly between two ships may seem fair, yet keeping both ships in service longer can delay a third vessel that needs a berth. The time at which a ship leaves can matter more than how busy every crane appears at each instant.
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An inbound flight is late, and some passengers are trying to board a departing connection. Holding that outbound aircraft could save their trip, but it also delays the people already aboard and may cause new missed connections farther down the route.
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