My headphones have a long cord that often ties up around my chair legs and get tangled. I designed this to help hold the long cord against the underside of the desk.
It really only works for my desk as the width is specific to my desk. other desks will have different widths, but I am sure other people can use the concept to help generate their own designs for their personal desk.

If you want to alter for your desk, then cut and change the length of the short edge to match your desk.