Product review (4 stars): The product is good,  But, I found that I didn't really need it.
I wanted to push my clothes dryer as close as possible to the back wall. The tight bend in this elbow will allow you to push your dryer closer to the wall without kinking the exhaust hose. This elbow is designed to be attached to the back of your dryer, not to the wall vent. But I guess you could attach it to the wall vent if you wanted to.  After I had bought this item (along with a new, semi-rigid, flexible exhaust hose), I found that I could bend the semi-rigid exhaust hose at an angle that was just as tight as this elbow... with no kinks! If your exhaust ducting is made of thin material(as so many are), you may not be able to create a tight bend without creating a kink.  Also, if your exhaust ducting happens to be rigid (non-flexible), this elbow will come in handy because of it's tight bend. To reiterate; if your exhaust hose is semi-rigid and can be bent into a tight angle without kinking, you can probably get by without using an elbow such as this one.  But, if your flexible exhaust hose is wimpy, this elbow will allow you to push your dryer closer to the wall without having to bend the hose too much.