You can use this to add a new Scale command before the currently selected command in a shape's command list. (Position of the command in the list will have an effect on its spatial consequence.) This new command will start out with its parameters randomized, but you can change them to whatever you want.
Each shape in a design maintains a variable-length list of operations in an internal language. This list can be modified in mutation to lengthen, shorten, and recombine with others. These commands are run on each shape as it goes from genotype to phenotype.
The Scale command scales a shape independently along the X, Y, and Z axes. It takes three parameters, one for each axis.
Note: AgencyGP's Z dimension is up/down. It corresponds to Maya's Y dimension.