How often should the vent system and dryer cabinet interior be cleaned of lint buildup?

Lint should be removed from both the exhaust vent and the inside of the dryer cabinet at least every 2 years, or more often depending on dryer usage. Cleaning of the dryer cabinet interior should be done by a qualified appliance servicer or ventilation system cleaner. Additionally, you should remove lint and debris from the exhaust hood regularly and use no more than four 90° elbows in your vent system to maintain good airflow. (Pages 5 and 13)