For me the one big advantage is time - I don't have to actually show the property with my Realtor, he will put a lock box on the door and show the place at anytime. This frees me up to work on other things, I do also work on filling the vacancy myself at the same time, I will list it with my Realtor and then work to fill it myself. I have found that the Realtor route opens up a new pool of candidates to fill my vacancy.
Realtors frequently get a bad rap for their services and often times they rightfully deserve it. In El Paso County, CO, we have a population of 655,000 people and almost 3,000 Realtors... That means almost 0.5% of the population has their license. With that many people calling themselves a Realtor, you're bound to find a bad apple or two... Actually I take that back. In my opinion, there are many bad Realtors for every good 1. You just need to find a good one, and don't expect it to be easy.