Musicians and singers use accompaniment CDs to replace all the other instruments in their songs. They can be used during concerts, auditions, or by street performers who need accompanying music to perform. The CD replaces backup singers and other musicians.
Many sheet music books also come with an accompaniment CD. The CD usually features an expert playing the sheet music pieces. The CD is provided so that the user knows what the sheet music sounds like, and they can also play along. Some accompaniment CDs contain a second part of a duet, for example, so the user can play the first part along with it.
Some books, such as children's books, may come with a CD that features a storyteller reading the book aloud. This can be helpful to a child who cannot read, or for a child just learning to read to follow along with the book.