Powers Your Body
The glutes are known in fitness circles as your body’s engine, not only because they’re the largest muscle group in the body, but also because they’re involved in most athletic functions, says Bret Contreras, C.S.C.S., coauthor of Strong Curves: A Woman’s Guide to Building a Better Butt and Body. The glutes produce four distinct actions: extending the hips, swinging the leg outward, rotating the leg laterally, and tilting the pelvis backward. “Strong glutes increase your force and power during everything from sprinting, jumping, and squatting to climbing, swinging, and cutting from side to side.”

Protects Joints
A stronger butt can mean healthier knees, as well as a pain-free lower back and hips. “The glutes pull your femur [thighbone] rearward during hip extension, which keeps the bone centered in the middle of the hip socket rather than sliding forward and causing hip pain,” says Contreras. “And strong glutes ensure that the femurs track properly over the toes when squatting, jumping, and landing. In other words, it prevents your knees from caving in toward each other, which is a major player in knee pain and injury.”

Source: http://www.womenshealthmag.com/fitness/toned-butt