The idea is indeed wacky! Yet, there is a purpose behind it all!
In our high tech, fast paced world many people believe that today's children have excellent fine motor skills as a side effect of all of the touch screen technology they use. Most children use their thumbs and pointer fingers for their touch screens. In working with a musical instrument, musicians use ALL of their fingers. We as music instructors, want our students to be able to move their fingers independently and with ease. Our bodies are designed with weaker middle and ring fingers which makes playing the piano with an even tone challenging.
I have had the honor of working with many students over the years who can understand music concepts beyond what their fingers allow them to play. I have added many exercises from books such as Finger Power, Dozen in a Day and Hanon. Yet, manipulating modeling clay, "Playdough", "Silly Putty", "Thinking Putty", etc. can help students beyond what a method exercise book can do.
So the next time your student is not so excited about practicing his or her traditional lesson assignments, set out some clay or putty and see if that can motivate those fingers to move!