I removed 6 of mine today. Started the car and the remaining ones opened and closed. I drove to work where i normally get 31 mpg stop and go. I got 35 today with less turbo surge and the car will do pulls all day longThe shutters close to provide better aerodynamics for fuel economy purposes. The downside is that when they are closed, they block the intercooler from receiving cool air. This means that warm air is being forced in to the engine as opposed to cold air which compresses better (air molecules and all that).
Now, unless your running WOT all of the time, I doubt you'll notice any difference really. And even if you are running WOT, the shutters should theoretically be open unless there's some sort of malfunction