What is the purpose of using Relation Command from the tool bar in Pro-e software?

make the design more easier and professional

The Pro /E is a fully parametric  CAD program .  The geometry of features (e.g., holes, slots) on a part have to be fully specified in terms of size, shape, orietation, and location. This specification allows the user to write equations (i.e., relations) which decribe how features on individual parts or multiple parts should relate to each other. For example, in an engine, if the diameter of the piston is increased or decreased, the corresponding engine block is automatically modified to match the specifications of the new piston.