Lint collects in the dryer venting

As lint collects in the dryer venting, the airflow will begin to slow allowing moisture from the dryer to condense inside the vent. This will collect in the elbows and low spots of the vent run, which will oxidize the steel duct which will eventually fail. Once the venting has failed, the airflow form the dryer will begin to occupy whatever space the opening resides be it under the home, in the wall, or maybe the space between floors. You may never know there is a problem until it can only be repaired by a vent replacement.