Basically, if you have two ears with hearing loss, and if both ears can benefit from hearing aids, you generally will do much better with two hearing aids.  It is important to realize there are no " normal " animals born with only one ear. Simply stated, you have two ears because you need two ears. If you try to amplify sound in only one ear, you cannot expect to do very well. Even the best hearing aid will sound " flat " or " dull " when worn in only one ear.

There are many advantages associated with binaural (two ear) listening and importantly, there are problems associated with wearing only one hearing aid.

Localization (knowing where the sound came from) is only possible with two ears and it is just about impossible with one ear.  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 impacts how well you hear in noise because binaural hearing permits your brain to selectively attend to the desired signal while " squelching " or paying less attention to, undesired sounds -- such as background noise.

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 much easier while using both ears. Additionally, using two hearing aids allows people to speak to you from either side of your head - not just your " good " side!

People generally cannot hear well using only one ear. 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 recognition ability more quickly than the ear wearing the hearing aid.

(by sicologic.com)