According to Consumer Reports more than 15,000 fires a year start in laundry rooms in the United States. From that, there are an average of about 10 deaths and $97 million dollars in property damage. Close to 4,000 of these fires are due to build up of lint in dryer vents when people don't clean them.
Dryer ducts that create the most problems are the foil and plastic ones because they have a tendency to sag which allows lint to build up at low points, especially if they have ridges which makes it easier for blockage to occur.
All dryers vent their exhaust along with some lint through a duct (commonly referred to as the" transition tube"), that attaches from the back of the dryer to the wall. Metal ducts, either flexible or solid are much safer because they don't sag so lint is not as likely to build up and create blockage. If a fire does occur, a metal duct has a far greater chance of containing it over a foil or plastic one that will melt and spread the fire throughout your home.
Repairs on dryers can be a headache as well. There is an element inside the dryer that heats the air to dry your clothes. Lint blockage in the vent can cause that to fail. When you have that happen, you're either looking at a repair bill for your dryer or having to replace it, thus creating a major expense you don't need.
No matter what kind of duct (or transition tube) you have attached to your dryer, you should have it cleaned regularly. In addition to that, you should clean the lint screen every time you use your dryer. This will not only reduce the fire risk, but will use less energy reducing your electric bill and dry your clothes much faster.
Transition tubes are shown below, ones that are more preferred than others.