In my experience they keep the wind off your legs as well as the rain if the vents are closed. On my '14 Limited the vents can be angled to push air flow straight through or towards the engine. I either open them full or closed fully.
They take the wind pressure off your legs and increase your comfortable calm air pocket. Personally, I like they way they look too. I think they balance out the rest of the body work.
I like the looks of em, they add some degree of protection, (ever been hit by a rock or other hard object) and it gives me a place 2 more speakers, oh yea good sound. That's it.
...after moving from the Road King to a Bike with Lowers the first noticeable thing was getting to my Destination with dry feet on a rainy ride - agree with OldHippie great sub speaker mounts.
Having rode with and without, I think they are next to useless. Might keep your boots a little dryer but thats about it. Don't do anything for you your legs. As a matter of fact when my wife and I get in the rain my legs are dryer than hers. Seem to direct more air in your face also. And they look bad too. Just my opinion.
Love them! Not only do they really change the look of the Road King, they offer great protection from the elements, as well. Now, I have only had them on my 2013 since mid summer, but I can attest from personal experience that they really add the wanted protection from the elements I was hoping for. They may not be for everybody, but I am very happy with mine. If I had to offer a piece of advice, it would be this.... If you add them to your touring bike, make sure you add a set of hyway pegs as well, because there WILL BE times that you want to get your feet out from behind them. Your feet (especially your right foot) will be warmer than you are used too, once you install lower fairings. Especially on really hot days.