If it were so "immaterial", why does this forum section exist?
I especially like "weedwhacker" claims of the "turbine cycle" which pumps bleed air into the cabin... it contributes to the old saying, "Having little knowledge is more dangerous than having none..
If the air you breathe in the cabin came off the "turbine cycle", you'd be dead before you reached 20,000 feet.
In fact, the air you get in the cabin comes off a compressor section,,, it is super clean. Any air from a "turbine" section is filled with CO after being fried in the combustion chambers.