"But I ain't no engineer"

We agree. LOL

Spend some more time re reading Wiki:

"Compressible aerodynamics[edit]
Main article: Compressible flow
According to the theory of aerodynamics, a flow is considered to be compressible if its change in density with respect to pressure is non-zero along a streamline. This means that - unlike incompressible flow - changes in density must be considered. In general, this is the case where the Mach number in part or all of the flow exceeds 0.3. The Mach .3 value is rather arbitrary, but it is used because gas flows with a Mach number below that value demonstrate changes in density with respect to the change in pressure of less than 5%. Furthermore, that maximum 5% density change occurs at the stagnation point of an object immersed in the gas flow and the density changes around the rest of the object will be significantly lower. Transonic, supersonic, and hypersonic flows are all compressible."

The word "arbitrary" stands out above, and the "compressibility" expressed is in terms mainly of aircraft aerodynamics, engine nlet intakes are much more responsive/sensitive to very low pressure changes relating to the original question posed, "fact or fiction", not "worth it or Not"