This in-line volume control It allows you to fine-tune the volume coming out of the source and fine-tune the volume to just the right amount.
I use this for instance on United Airlines flight seats. Because of the sensitivity of our units, you can not reduce the sound coming through the plane system low enough to get the power humm to stop, and the lowest setting just too loud.
By using this in-line volume control you can turn the volume coming out down to your ears and up from the seat to cancel the low volume humm created by aircraft.
Additionally, you can put this in-line volume control with your Big Ears and turn the volume up and down without having to find the device itself and adjusting it there.
As a bonus, it will also come with the old school 1/4 inch standard headphone jack that the 3.5mm will plug into.