Grant Erwin writes:

That's interesting. How did you come to that conclusion? Applying that
to my hypothetical situation of an airflow of 10 cfm @ 180 psi
regulated down to 90 psi, that would yield about 13.7 cfm at 90 psi. I
suppose we're assuming constant temperature throughout.

No, you fundamentally misunderstand.

CFM (or SCFM) has nothing to do with pressure. It is a measure of the
flow rate of air, expressed at atmospheric pressure.

The CFM (or SCFM) going into your tool is the same as the CFM (or SCFM)
exhausted, even though the power has been spent. Think of the CFM as
the amount of exhaust (free air) that comes out of the tool.

An air regulator is not at all analogous to an electric transformer.
The proper analogy is to a three-terminal voltage regulator. Energy is
lost; that is how the regulator works. The CFM (or SCFM) on either side
of the air regulator is necessarily equal. The pressure drops. Power
is lost and turned into heat.

SCFM is just CFM measured with a standard temperature and humidity in
the free air. Hotter or wetter input air will degrade the compressor
performance. Cooler or drier input air (than the standard) will improve
it.

An "SCFM" (standard CFM) is a CFM produced with input air at 68 deg F
and 36 percent relative humidity.

I have a 600 CFM compressor (!) in my garage that uses only 1/3 HP!
Read how:

http://www.truetex.com/aircompressors.htm