That really depends on what kind of noseband you are talking about.
The thick nosebands in western riding are referred to as tie-downs. They are used in speed events to give the horse something to brace against to help him keep his balance. Although a lot of people use them on high-headed horses thinking that it will help keep the horses head down. That ususally only makes the problem worse.
Then again, there are bosals that look like nosebands. They are basically a bitless bridle.
I am unsure to the real purpose to the english noseband except when people use them to clamp the horses mouth shut that is often seen in jumpers and dressage. An english rider will have to help you with that one.