Don’t wait for the annual audit to identify problems, good systems continually look for ways to improve. Why not have a fresh set of eyes to identify problems for you.
It’s not a good idea to have the person who set up the system also audit it.
An independent person can pick up on deficiencies in your systems before the External Auditor.
Blind Spots
Over time you become immune or blind to issues around you, a fresh set of eyes can assure things are not overlooked.