The shape of the ears is supposed to enhance your hearing. You may notice some very minimal improvement but the research on this is minimal.  There are times when you setback the ear that can cause the cartilage to impinge the ear canal and this can actually worsen your hearing to a degree.  Otoplasty that can help your hearing is when it is done in conjunction with more complicated surgeries for a condition called microtia.  This is when the ear is rudimentary in form.

What can come with this is canal atresia when the ear canal is very small and unable to conduct air but most of the time maintains the ability to hear through the bones of your skull, meaning the nerves and some of the bones that conduct hearing to your nerves are still functional.  Otoplasty for microtia is part of a bigger plan to open up the canal and allow for air conduction of hearing.