In this example of a mannikin model, each limb needs to be rotated to pose the model. For example, the lower leg surfaces need to behave like a single object, and be able to rotate around the knee. Grouping provides a single pivot point that allows all the surfaces in the lower leg to rotate as a single entity.
Here, groups have been made and carefully named, and then grouped again to form a complex hierarchy simulating the motion of the body. A simple example would be a car door.
