I've had an exhaust brake (turbo brake) on my 2006 Duramax for the past 7 years. My experience with driving while on is that fuel mileage is decreased some. When I could be coasting down a hill, it slows me down to where i have to press the pedal to go.
I have had absolutely no negative effects having it on while not towing. And yes, it does help slow the truck down going down hills or coming to a stop.
All the arguments not to use it while towing are nill. To call someone stupid or lazy for using the turbo brake shows their ignorance on the subject. It takes effort to turn on the EB every time so there goes the lazy arguement.
The EB doesn't come on until the engine reaches around 1,800 rpm's. So the EB doesn't always come on as soon as the pedal is lifted.
Turbo vanes are all over the place from the moment the truck is started (at least on most '06 and up diesels). The carbon build up isn't something to worry about. At least not from the vanes not moving.