Localization (knowing where the sound came from) is only possible with two ears. Localization is not just a sound quality issue; it may also be a safety issue. Think about how important it is to know where warning and safety sounds (sirens, screams, babies crying, etc.) are coming from. Using both ears together also impacts how well you hear in noise because binaural hearing permits you to selectively attend to the desired signal, while downplaying undesired sounds such as background noise.
People cannot hear well using only one ear. There are studies in the research literature that show children with one normal ear and one “deaf” ear are ten times more likely to repeat a grade as compared to children with two normally hearing ears. Additionally, we know that if you have two ears with hearing impairment, and you wear only one hearing aid, the unaided ear is likely to lose word understanding ability more quickly than the ear wearing the hearing aid.
Binaural hearing allows a quality of “spaciousness” or “high fidelity” to sounds, which cannot occur with monaural (one ear) listening. Understanding speech clearly, particularly in challenging and noisy situations, is easier while using both ears. Additionally, using two hearing aids allows people to speak with you from either side of your head – not just your “good” side!