It is recommended to clean the lint trap after every cycle use. If you don’t, it will make your machine work harder to dry your clothes. This lint can become a fire hazard. It is recommended a yearly check on your dryer vent to remove lint build up and any other debris that may get into your vent. (Bird Nest).
It is also recommended that every few years the dryer be taken apart and cleaned of lint build up inside the dryer casement.