If you have hearing loss in both ears, it is in your best interest to have two hearing aids for the following reasons:
WE NEED BOTH EARS TO LOCALIZE SOUND
To be able to hear where sound is coming from, we need balanced hearing from two ears. For example, when more than one person is in a room. We are able to detect who is speaking because the sound from the speaker will reach the closest ear first. This mechanism is used with any sound such as an approaching car or even the yell of 'Fore!' on a golf course. With both ears you can locate sounds not only horizontally, but also vertically, 360 degrees in all directions.
STEREO SOUND
Stereo listening gives depth perception. Anyone who has enjoyed music in stereo, compared to mono, knows the difference. Mono makes sounds seem shallow, flat, and unnatural. Your brain has the ability to hear in stereo, but to do so requires that sound be delivered to both ears. Not only are sounds more natural, but they can be understood more clearly.
POLITENESS
People with only one hearing aid can be perceived as rude and not respond to someone who is speaking on theside of their unaided or 'bad' ear.
HEAR BETTER WITH LESS VOLUME
Due to a lack of hearing in one ear, individuals will feel the need to turn up the power on the hearing aid in their fit ear. This will let in more background noise and will therefore be more distracting and stressful. A voice barely heard at 10 feet with one ear can be heard up to 40 feet or more with two ears.
AN UNAIDED EAR LOSES SPEECH CLARITY
When a person with hearing loss in both ears wears a hearing aid in only one ear, the unused ear tends to lose its ability to understand speech clearly. Once an individual is fit with a single hearing aid, people no longer need to speak as loudly as before. This means that the unaided ear won't receive speech signals and will lose speech discrimination as a result
CUSHIONS LOUD SOUNDS
Sudden loud sounds lose much of their jarring effect when divided between two ears.
AUDITORY INTELLIGENCE
The two halves of your brain work in harmony to give you an auditory picture. There is a complex pattern of stimulation including sound signal crossover that makes up auditory intelligence. The two halves of the brain are required to work together to produce auditory intelligence much like the two havles of the brain convert two images from both eyes to produce one picture. Two hearing aids help the signals get to both sides of the brain, thus increasing your auditory intelligence.
For more information please read the following article from the Maryland Hearing and Balance Center. Do I really need two hearing aids?