Air rights aren’t invisible if you are a developer. There is money in being able to build bigger and taller.
I only know of one such TRD in Atlanta and that was for the air rights above the Margaret Mitchell House on Peachtree Street. I’m not sure if those are still in effect as the building they were to be applied to was never constructed….a high-rise apartment building on 13th Street. I wonder whatever happened….
See on www.nytimes.com