If they do it themselves they can have more control, perhaps save a little money, take extra pictures, and get it done more often and quicker. The main downfall is you have to have someone to do it and you have manage that person to make sure it gets done.
If they pay someone to do it they have more of a guarantee that it will actually get done. That is the primary benefit in outsourcing it.
At the end of the day, the most important thing is that it gets done. Ultimately that is all that matters. If it doesn't get done, it will hurt the dealership's sales.
Amen, brother.