the presence of fuel (ie mass or weight) in the wing, acts to reduce the bending loads on the wing in flight
At one stage the C-130 was having wing fatigue issues, in order to reduce the bending moment, while investigations took place, an instruction was issued to keep a certain substantial minimum amount of fuel on board (in the wings).
I was watching a documentary on YouTube
Recently watched a few aviation shows on TV and have had an interesting education. Learnt that a Cessna 310 uses kerosine as a fuel, the proper name for an engine is a "thruster", and a A320 and 737 are one in the same aircraft. Pity that shows dedicated to a subject are so poorly researched, but then, it's just entertainment to an ignorant audience.