The moon gives us the tides, it protects us from space rocks, it is just the right size to give us eclipses, it is way bigger and way lighter then it should be.
Some guys have been speculating that the moon is artificial because it works so perfectly to give the earth and humans a number of advantages which other planets do not have.
Of course then they have to try to come up with who made it.
That is when it gets weird.
The biggest thing is the tides. The tides help to keep the waters near the coast clean and oxygenated.
Likely bubbles, rather than strictly "hollow".
The moon gives us the tides...
Regular tides improved the chances of Life forming on Earth.
it protects us from space rocks
Along with Jupiter's massive space presence, even more reason for Life to be sustained on Earth.
(And less reason for Life to appear elsewhere in The Cosmos).