Loading a 777-300 ER can be an exercise in optimizing revenue. Cargo v. leaving people behind. We regularly carry over 100k in cargo, and have more cargo than we do weight available. Load planning and the station work together to maximize the money. They often "save" some weight for last minute changes which annoys me, because that means we leave people behind needlessly. You can work with them and be proactive to get more people on, but that seems to be the exception rather than the rule.

In short, it's all about the money, and the cargo contract. Can we leave some non-priority cargo behind today and take it tomorrow? Lots of decisions to make. And yes, they do ask us to reduce fuel once in a while to get more cargo on. So lots of moving parts, hence the load planners.