The wings give you extra leverage for a tight fit, while the flange distributes pressure evenly across the mounting surface without the need for a separate washer. These nuts are often used to secure screws in oversized or irregularly shaped holes since the flange covers a larger area than standard nuts. They are the easiest nuts to twist on and off, so they are ideal for fastening parts that need to be frequently disassembled, such as access panels and covers.