When Designs are inherited via Mixins rather than copied, future changes to the mixed-in Designs automatically ripple through the Designs that inherit from them, thus eliminating what can be a very large and tedious maintenance problem.
In the Table Project, whose Children have inherited Designs and Rules from the Block Mixin, inheritance means that your new Table Design's components will automatically have all the Rules that are contained in the Block Design. Without inheritance, you would have to painstakingly create Rules to capture height, width, length, points of origin, and many other attributes of a 3D block.
Above, all but 3 of the rules contained in Block. Sorry, had to make it very small to get them all in.
Inputs (Parameters), Geometry, rendering and much more become available to your design when you mix Block into your Design. In other words, your Design inherits this wealth of re-usable content.
