IEMs allow the singer and sound engineer to communicate during recording sessions and performances. For example, a sound engineer might need to relay technical information to the singer to make any adjustments to the playback sound. IEMs also provide information to the singer onstage telling him if there are lighting or pyrotechnics problems and/or special guest appearances, as well as any information regarding the facility and public safety.
IEMs are also used a safety measure to protect the singer's hearing. Singing in front of large crowds of screaming fans and in front of multiple amplifiers that carry and enhance the sound of guitars, drums and other instruments for long durations, singers are susceptible to developing ringing ears, hearing loss and/or other auditory problems. IEMs protect the singer's ear by filtering and reducing the surrounding sounds that can cause extensive and often permanent hearing damage.
Ironically, IEMs are used by singers during live performances in order to hear themselves. The IEM allows a singer to determine whether he is singing in key and in tempo with the music. They also let a singer know if he is singing too quietly or too loudly. Every venue, in terms of the layout and crowd size, presents different sound dynamics, so IEMs are an important tool to help the singer gauge and adjust his performance as needed.
IEMs also allow the singer to cue his band as to what direction the musical performance should take. This requires the entire band to have IEMs and a cue system prior to the actual performance. Cues help band members keep pace with one another and make impromptu musical arrangement changes such as shortening or lengthening a solo.