Many people use headphones to the watch movie as well as to listen to songs. You must be aware that there are (L) and (R) written on the headphones but have you tried to know what is the reason behind it.
You must be thinking (L) and (R) are for plugging to left and right, you put your headphones in your left ear and right ear. Have you ever noticed that what happens when you put (L) headphones in your right ear and (R) headphones in your left ear? It gives you the same music or dialog, then Why are (L) and (R) is written?
Headphones pass the sound from the different channel, In fact, they are not unnecessarily written. Actually, there are many rational reasons behind it. One of the main reasons is “recording“, if the sound comes from the left you hear it in the left channel and it will be louder on the left and lower in the right channel.
Another reason for having left and right channel in the earphones is it’s easy to make the listener hear the sound by single channel one after the other rather in both the channel. The difference between them is easy to recognize.
Several songs have Loud Musical Instruments (eg. Tabla) and Soft Musical Instruments (eg. Flute) in one music. So in order to avoid the loud music suppressing the soft music, they both are played on different channels.
Have you ever seen a movie through laptop or phone using headphones to listen audio? If yes! Then maybe you have noticed that the sound of the vehicle is your headphone coming for months your left will be more in the left channel and less in the right channel. This is to make the listener the sense of actually being present at the scene.