Some tasks can be more easily accomplished using links while others are easier with parent/child relationships. You could use either a link or parent in the example you've provided. With parent/child relationships you can move the objects in their own local or parent coordinate system. The
coordinate systems tutorial covers this topic. With links the source object's transform (position, orientation, scale) is applied to the destination object. However, there are operations that can be applied on the link to modify the source transform before it is applied to the destination. For example, different combinations of position, orientation, and scale can be applied to the destination object using masks and offsets between source and destination can be defined.