They should. Getting the correct amount of fuel load is essential particularly on long haul flights. They also have to factor in whether they might need to dive

They should. Getting the correct amount of fuel load is essential particularly on long haul flights. They also have to factor in whether they might need to divert on to another airport if their destination is shut for some reason and / or there are storms that needs flying around. Get the fuel load wrong and someone's going to have to ditch the plane or glide the rest of the way to the nearest airport. The Gimli glider incident comes to mind here. https://en.m.wikipedia.org/wiki/Gimli_Glider https://en.m.wikipedia.org/wiki/Gimli_Glider