At this point, you've created a variation of your original part, but it's probably not exactly what you want. One obvious flaw is that the holes in the plate are not constrained to adjust along with the perimeter. Although you could move them by giving new values to their dimensional constraints (just like you did for the length and height of the plate), this is not efficient, because you would have to calculate and re-enter these values each time you generated a variation with different dimensions. Parameters provide a much better method for accomplishing this. Parameters allow you to use expressions to define relationships among constraints.