My experience is on non FBW Boeing types [737 757 767) Advice sought from Boeing and published in the Company’s Training Guidance is that fuel asymmetry poses no handling problems, even with one wing full and the other empty. The primary purpose of fuel balance limitations on Boeing airplanes is for the structural life of the airframe and landing gear and not for controllability. A reduction in structural life of the airframe or landing gear can be caused by frequently operating with out-of-limit fuel balance conditions. Lateral control is not significantly affected when operating with fuel beyond normal balance limits. The primary purpose for fuel balance alerts is to inform the crew that imbalances beyond the current state may result in increased trim drag and higher fuel consumption.