Occasionally, water can accumulate within your dryer vent system so that there is wet, sopping lint. Normally, the moist air from the dryer dampens the dryer vent ductwork, the moisture in the exhaust is largely brought to the exterior, and the dampness remaining in the duct evaporates away. When there is a significant blockage or restriction such that the dryer is unable to bring the moisture outside, the water accumulates within the duct and creates problems. First, it can be very difficult to clean the dryer vent (higher cost) and can also require an additional cleaning a week or two later (extra cost). Second, large amounts of condensed water can leak out of the duct and damage your house. Third, this same water can corrode the galvanized metal ductwork, especially if it doesn't have a way to leak out of the duct. This can require anything from a more isolated repair to a complete dryer vent replacement. This can all be avoided by simply staying up on regular dryer vent cleanings. All these problems become quite costly and can be mitigated by proper maintenance.