What might be a consequence of having outboard fuel tanks filled?

Having outboard fuel tanks filled can indeed help reduce the stress on the spar and mitigate the onset of flutter. This is because when fuel is stored in the outboard tanks, it helps distribute the weight farther away from the aircraft's center of gravity. This distribution of weight can enhance the overall structural integrity during flight since the added mass at the wings' tips can help in stabilizing loads and reducing bending moments on the wing spar.

Furthermore, by keeping the weight farther from the center of the aircraft, it may assist in lowering the risk of flutter, which is a potentially dangerous oscillation that can occur when there is an imbalance in aerodynamic and inertial forces. This particular configuration supports the aerodynamic performance and structural safety of the aircraft, making the aircraft more stable during various phases of flight.

In contrast, while increased weight does occur with filled fuel tanks, the main focus of this question centers on the aerodynamic and structural implications rather than just weight alone. Other options do not capture the primary benefits associated with fuel management strategies regarding structural integrity and safety implications in this specific context.