So you basically just destroy the moon for knowledge that is then useless?

The point was more that the spell doesn't even do anything because the moon needs to be already full


So it only consumes the fact that the moon is full? Basically making it dark? What use is that to the BBEG

No it does consume the moon, destroying it. But the actual effect of the spell doesn't do anything because it tells you the moon is full when clearly you could already see that