this is for me like to rent a piece of land on the moon: and what are the benefits of it? May be in 200 years, we can build a city on the moon and can make our holiday over there, but one thing is clear; even I own it, I will not see it

1.
This is not so. You are not careful. You completely own a real section in the sky, with real coordinates (the same principle as with land plots).
2. Advantages are more than obvious, at least it is:
monetization,
collectible and
entertainment.
For detailed understanding I recommend to read White Paper:
goo.gl/FHT5DS How are saying that he completely own a real section in the sky, when you just use augmented reality to display customized word !
Out side your app, he owns nothing, therefore he don't own a real section in the sky, he just own it on the app. and actually other app owner can sell that same section in the sky for someone else.