Building codes do not require the decking of the roof and the facia board to meet. This gap allows wildlife to enter your attic easily.
Rodent droppings carry diseases that are harmful to humans. The fumes created by rodent dander, feces, and urine make the air toxic, and can aggrevate asthma and allergies.
Nesting rodents can destroy your attic. They pull down insulation, damage drywall, and penetrate air ducts. They will also bring in leaves, twigs, and acorns.
The greatest threat to your home are chewed wires. Chewed wires become a very dangerous fire hazard and damage created by fire from rodents is not covered by homeowner’s insurance.