What would be the exact benefit of using that special mount they show?
Mounts give you a place to store the the "pigtail" that comes off the back of the camera. The camera's weather-resistant ethernet connection is a lot wider than an unterminated ethernet cable, so if you mount the camera flush on something, you have to drill a much larger hole so you an stuff the pigtail (which is the weather-resistant ethernet connector + the 12v plug <that you won't use if you use PoE>) through the wall/soffit/whatever vs. drilling a much smaller 5/16" hole to pull an unterminated ethernet cable from inside through (then terminating it on the outside of the house, then stuffing it and the water-resistant connector in a mount like this one).
Not the case with this picture, but mounts can offset the camera from a wall which can help reduce IR when the camera is mounted directly to a wall and is aimed right down the side of the wall (or has something over it, like a soffit). IR washout can be extremely bright, which if included in the camera's FOV will usually cause the camera to try and compensate for it which causes the rest of the scene to become too dark.
Appearance. Some folks like the overall esthetic of a mount (especially that particular mount) vs. having the camera directly mounted to the wall.
Flexiblity. Mounts usually have a bunch of different predrilled holes to accommodate many different camera models. So this person could swap the 5231 out for a bunch of different cameras without having to mess with the wiring or how its mounted to the house. The camera mounts themselves are different sizes. i.e. I just swapped out some 5442s for 5231s and the hole pattern for the mounts are different, so I now have six screw holes in my soffit at the two locations where I did this swap (three from the 5231s, three from the 5442s).
IMO, I can't think of any reason why you couldn't mount a 5231 to the wall directly and aim it like this 5231.