Speech intelligibility is improved in difficult listening situations when wearing two hearing aids. If you are only wearing one hearing aid then it is harder to hear someone standing on the other side of you in a group setting. By wearing two hearing instruments, you increase your hearing range from 180 degrees reception, with just one instrument, to 360 degrees.
This greater range provides a better sense of balance and sound quality. When in a social or business setting, it is important to be able to hear speech from everyone in the group and wearing two hearing aids increases the chance of speech understanding.