Dryer vents accumulate highly flammable lint which can be extremely dangerous. Failure to clean out lint is the leading cause of dryer fires. Leaving the dryer vents uncleaned also causes your dryer to use approximately 30% more energy, costing you even more money. If the dryer vent is full of lint, it can cause the duct hood flap to not open and close properly. If its even slightly open, this can be an invitation to animals to make your vent their new home.