Mold is present long before it "grows" big enough to be seen by the naked eye. The invisible parts of the mold fungi are carried through the air like tiny dandelion seeds, landing on the surface of many potential food sources.
Your Health is Affected
You can't find a doctor who says mold in a home is good. It's all bad, especially to children and the elderly. Besides irritating people with asthma and mold allergies, studies show that prolonged exposure to mold can actaually cause asthma.
No Laughing Matter
It's just a matter of time before a damp crawl space rots out your floor, and spreads throughout your whole crawl space.
Mold Growth Doesn't Just Happen Overnight
It takes time for mold to grow. Once mold has grown large enough to be recognized visibly, a much more serious moisture problem exists somewhere.
Mold, Rot, and Critters
Beyond the cold and the moisture, and the dirt, it's the living organisms in your crawl space- the fungus and the insects- that could end up earing the support beams and joists in your crawl space, causing foundation issues and other big problems.