". . . How does flying over a roof help sell a home? . . ."
If the Parcel involves more than a few acres, an aerial is helpful to get an orientation for the Home's positioning on the Lot, its Boundary Lines; the surrounding area and any local geographic features.
I have a Pilot Friend who has to put in his flying hours each year so I'd develop an itinerary of 100 to 150 properties to photo (my own listings and some of the competition's); pay for the fuel, and go fly over them at peak foliage season.
I might take 500 to 600 photos in the course of 2-3 hours, not covering the same territory twice.