- The tides would change or probably completely diminish, affecting ocean currents. This would cause major climate changes eventually.
- The stability of the earth's axis would be affected and it's rotation speed would change. Meaning; no more 24 hour days.
- The moon actually acts as a shield and/or bait and catches meteors before they enter the earth's atmosphere. So that's a problem.
- Nights would be a lot darker, seeing that the moon acts as a reflector for the sun.
- The moon tugs on the Earth providing the 23.5 degree tilt necessary for habitable weather, and other means of life. Without this tilt, the earth's climate would not exist as we know it today. As an example; the equator would bake.
On a more on-topic and serious note;
Nagato claimed that the Sage had used Chibaku Tensei to create the moon and it didn't seem to take that long for him to create that 1/18 scale of it back in the Pein arc.
Seeing that Madara was able to create two massive meteors, an endless supply of Mokuton, a number of other overkill stuff all accompanied by his Susanoo by only relying on his own chakra I think it's fair to think that he'd be able to create something akin to a moon with the help of the endless supply of chakra (aka the Juubi) he has at his will. :shrug: