Originally Posted by Jeff767

The above poster is correct. Delta's priority is revenue passengers and then revenue baggage. They are supposed to be the last two items pulled for weight after everything else. It's quite possible for a variety of reasons to have a international flight that can't carry a full load of passengers and all the bags even with zero cargo. The Airbus A330-300 is the worst for this. As a small example fuel loads on a long international flight can vary by as much as 50,000 lbs depending on winds and arrival destination weather. Making a fuel stop is generally not a good option since it means misconnecting every passenger. As mentioned crew legalities especially under the new FAR117 probably make a stop illegal.
Another aspect not mentioned is runway availability at the departure airport. If a runway is taken out of service and the aircraft is forced to use a shorter runway or one with more obsticles in the departure path max TO weight can be severely restricted. Both temperture and wind have a big impact. In short the maximum allowable takeoff weight for a given airport can very greatly day to day and even hourly and it's often beyond the control of the airline.