Airflow is a key fundamental of your dryer. Restriction of air flow can overheat your machine, causing unsafe and damaging effects. Dryers have built-in safety components that will shut down the heating process if this should occur.
If your laundry is damp at the end of the cycle or is taking to long to dry, this could be your issue. Make sure to clean your lint screen before each use and check for any damage. If you run water over the screen and it holds water, it is time to replace the lent screen. Also, check the venting behind the dryer for obstruction or damage. Make sure you are getting sufficient air flow coming out of your home where the dryer exhaust the air to the outside. If you have no air flow coming out or you are unsure for any reason, call a professional that can thoroughly inspect your venting.