Structural-aircraft-screws are not only stronger but the unthreaded portion of the shank serves as a bearing surface for the plate. Non-structural screws are fully threaded and may damage the hole, especially where there is high vibration or shear forces.
In the picture below, a fully-threaded screw has been used on an aircraft-spinner. Sharp screw threads are bearing against the spinner and wearing the hole. A structural screw with unthreaded shank would have protected the hole from wear, reduced cracking, provided a stronger attachment. But pretty and shinny won the day. Spinners are subject to enormous forces and vibration and should be attached with respect.
