In the field of mold making and casting, it is generally assumed that you make one mold of the original and are done with it. The same mold can be used to produce multiple castings as required.
However, experienced mold makers will be quick to point out that there are times when it is prudent to make secondary molds. Making a new secondary mold from the original mold (or subsequent cast) but with a different material will allow the liberty to use more types of casting materials.
The procedure for making a secondary mold is just like when making the original mold. Keep in mind that a secondary mold should be made only after the original mold or cast has cured properly.
In sum, secondary molds come with a lot of utility.