Some people prefer audio books to visual ones. Its a choice; there is no right or wrong in the answer. There are those who can do things while listening and that is an art in itself and many among these talented people like to listen rather than read. There are others who must juggle many roles in their every day lives and the joy of keeping one ear fixed in an audio book while performing other chores is a godsend.
Another amazing benefit is that those who are blind can enjoy the luxury of knowledge obtained from the world of books by listening alone and I know of at least one person who cultivates this as a useful tool to help him supplement his role as a chairman of his socio political group.