To understand the trade-off between a wing’s performance and its weight, you must be able to predict the aerodynamic loads and how the structure will react to these loads. This requires both an accurate flow solver and a structural solver, and automatic coupling between the two. The flow solver predicts the distributed aerodynamic loads (static or dynamic) and transfers these loads to the structural solver in the appropriate format to predict the wing deflections.
Most CFD tools used today do not provide an automatic coupling between the flow and structural solvers required for productive use. Therefore, most aerodynamic predictions assume a rigid wing — a significant potential source of error leading to overdesign and expensive fixes later in the process.