Moisture damage. When you grab that giant load of heavy, wet clothes out of the washer and shovel it into the dryer, you’re probably not giving a second thought to where that water is going. You’re just looking forward to the warm, dry, fresh clothes! However, typical dryers can expel somewhere around a gallon of water into the air with every load of laundry. If your vent is pointed indoors, this is bad news.
Fire. While you’re more than acquainted with the lint trap in your dryer, that’s not the only place that lint goes. As exhaust is pushed through the ductwork behind your dryer, it’s also pushing lint and other particulates through. If the duct is not pointed straight, the lint can get caught and is very flammable.