I’m unilaterally deaf, which makes it exceptionally difficult for me to localize sounds and also makes it impossible for me to hear sounds and dialogue that are coming from the wrong channel. I’m always relieved to find a ‘mono’ sound toggle in the settings because it allows me to experience the audio portion of the game as much as is possible.
Matthew Taylor, gamer

Unilateral deafness or other asymmetric hearing impairments can mean missing important sounds that occur only from one direction. A mono toggle gives the option of combining both audio channels and playing the single combined channel through both left and right speakers/headphones, meaning every sound is available from both sides.

Best practice example: Diablo 3