Runway length and current weather conditions can have a strong bearing on allowable weight both for takeoff and landings.

Jackson Hole WY is a good example of weather changing things quickly for weight limits.

Another time in leaving Salzburg Austria we had to take only enough fuel to get to Dublin before continuing on to LAX. Mostly because the plane was stuffed full with passengers and baggage combined with a short runway.

In my experience there are can be variables that impact airlines decisions.

Guido88