The discovery of the CMBR did not lead to the theory of the Big Bang. But astronomy in general certainly did, for sure.

That doesn't really answer my question though, but that's probably my fault for using a word as subjective as "useful", so let me rephrase:

How has astronomical knowledge of the CMBR/Big Bang/Black Holes/Pulsars/Galaxies/etc. fundamentally improved the human condition? What specifically have we been able to do (not "know") that we would not have been able to do without terrestrial astronomy?