In this photo, you can see that the subfloor joists are now free of mold spots and fungal growth. The homeowners were excited that they would not have to smell mildewy, stale air anymore.
Why are they smelling mildewy, stale air? It's due to the "Stack Effect", where your home's pressure draws air up from the lowest floor of the house, in this case the crawlspace, and that air disburses through the home, until it flows out from the attic vents.