What is a unique factor that affects fuel efficiency not related to speed?

Aircraft weight is indeed a unique factor that significantly affects fuel efficiency, independent of speed. When an aircraft is heavier, it requires more thrust to achieve and maintain flight, which leads to increased fuel consumption. This is primarily due to the fact that the engines have to work harder to lift the additional weight, thus using more fuel per mile traveled.

In contrast, pre-flight inspections primarily focus on safety and operational readiness rather than directly impacting fuel efficiency. Cabin pressure adjustments are related to passenger comfort and safety, influencing the aircraft's pressurized environment rather than its fuel consumption. Lastly, passenger habits can affect fuel efficiency indirectly, such as through baggage weight or onboard behavior, but these are not as consistently quantifiable or significant as the aircraft's inherent weight itself. Therefore, weight stands out as the most direct and influential factor in fuel consumption.