Headphones are important sometimes.  They allow me to listen to an audio source without anyone nearby hearing.
Yes, I agree. They are especially useful when travelling on a bus or airplane.
They convert electrical signal to a corresponding sound.
Have you ever tried the version that vibrates your eardrum to create sound? I tried Google Glass and that is how it worked.
Google Glass
Google Glass is a brand of smart glasses—an optical head-mounted display designed in the shape of a pair of eyeglasses. It was developed by X (previously Google X) with the mission of producing a ubiquitous computer. Google Glass displayed information in a smartphone-like, hands-free format. Wearers communicated with the Internet via natural language voice commands.
Google started selling a prototype of Google Glass to qualified "Glass Explorers" in the US on April 15, 2013, for a limited
Headphones
Headphones (or head-phones in the early days of telephony and radio) traditionally refer to a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. Headphones are also known as earspeakers, earphones or, colloquially, cans. Circumaural (