Naturally when you are drying your clothes, they generate lint. You clean the lint probably every time you start the dryer. Imagine that lint is piling up in the dryer vent causing it slowly to clog. Moreover, with time the humidity and other causes get the lint to toughen up and stick stronger to the vent. Therefore, the more you use your dryer vent the more often you will probably need to clean your vent. Please do not procrastinate on the cleaning of the vent as it could just that easily catch on fire. Moreover, we strongly advise that every time you call for carpet cleaning or air duct cleaning, clean your vents. You could never be too cautious with this hazardous component of your house.