Lots of moisture
Lots of moisture can cause the insulation to get heavy enough to actually fall. This is not the biggest concern when it comes to moisture in the crawl space though, the biggest concern is that mold only needs a little bit of moisture and warmth to grow. The crawl space is the perfect environment for this.
The pressure
Once the floor joists get so warped, and start to fall apart this puts pressure on other parts of the home which can create major foundation settlement problems and lead to even bigger bills to fix.