What's the little plastic clip on the headset good for?
I actually find it very useful to clip around the buttons on my dress shirt. Depending on the amount of slack I want, I can pin it around different buttons.

It creates enough slack in the lines/wires that go to the ears:


reduction in cord noise carrying up into ear-buds
the mic in the right wire stays away from your body (better pickup and less noise
if the earbuds fall out of your ear, they don’t drop all the way to the floor 


It works perfectly (see yellow arrow in picture):