This is a topic I have discussed before, well many times before. Lets face it, there really is only so much I can say about dryer vent cleaning and the various pieces of that puzzle, but when I run across a visual demonstration of why dryer vent cleaning is so important, well I guess it is time to start talking up the topic again.
Your dryer needs airflow to dryer your clothes. All the hot moisture laden air than flows out the back needs to go somewhere and outside the home is the preferred destination. But sometimes through good intentions by builders or homeowners, that destination becomes a wall and unless periodic dryer vent maintenance is on your list of things to do, (if it is, you are among the elite 1%) that wall will only cause problems.
The reasoning is understandable. Dryer vents are a great source of lint (bedding material) and heat (this makes us warm) for woodland creatures like birds, and since they really have nothing but time on their hands, they will find a way to get into a poorly maintained dryer vent cover. So the solution is to put on a cage from the local big box store. But this has definite problems as demonstrated in the attached photo. Lint that should be blowing out of the ducting becomes trapped and thus begins the buildup inside the ducting.
And as the lint builds, it really has nowhere to go but to impact further into the dryer ducting and will untimely result in poor clothes drying on the cheap side, and and unexpected dryer repair on the more expensive side. The simple answer is to remove these cages if they are currently in place, and not to install them if you are thinking about it. The international mechanical codes specifically states screens are not to be used on dryer vent exhausts and for good reason. So do yourself a favor and have a look at your dryer vent cover. If you have a cage, get rid of it. You will thank me later.