The knowledge and experience you gain from working within a well-defined set of parameters, while expressing yourself from a range of different perspectives within those parameters, allows you to nuance your compositions more subtly, purposefully and in greater depth and detail
What creates a well-defied set of parameters? How would you know what is to hard and what is too easy in the process of making multiple variations of your piece?
About how many of each piece would we make in order to effectively improve?
How would you eventually develop and know what your signature style is? what if you don't enjoy that style of art as much as something else?
Does this text imply that you should do multiple pieces for EVERY work you create in order to improve? Wouldn't it be better to create only one piece and make it perfect in one shot t improve?
In order for an artist to create the "perfect" work, they need to patiently approach the work in different styles with different versions of the piece. This allows the artist to understand his or her signature style.