If you are talking about the damper on the baffle plate, it is used as a way to control the flow of the draft under the plate to allow for better control (tuning) of the radiant heat for more or less even cooking temps. helps eliminate hot/ cold spots.
well the more open it is, the faster the draft, the more uneven the temps. the more closed it is, the more even the temps. when i run the dimensions on a smoker I always include the minimum and the maximum openings for the damper. if it is closed too far, as you said, it will choke out the fire.
some guys spend a lot of time getting them just right then have a rail with set screws for securing them in place. On my build I am not securing them in place since it is a reverseflow/ tuner
The R/F cooker I built the Smokin'Ace's competition team does not have a damper at the end of the plate in my opinion it is not needed. Once the R/F plate and cooker are equalized during warm up the variation in temps is plus or minus 10° in a 60" span. My current build is a hybrid with plates to convert from tuning plate to R/f if I choose. I however prefer tuning plates because I want a hotter spot for chicken. Once you learn the cooker plate placement becomes second nature and there is no real need to lock them down. A while back I worked a cooker with hold down bolts on the plates and they were a pita to adjust you know hot cooker and hot plates plus smoke in your face is no fun I prefer to slide and go.
I hope this helps.
Here is a link to the R/F build. viewtopic.php?f=11&t=270
Also as I always say, the smoker is only 50% of the equation the other 50% is the guy running it. After you spend time running your smoker as KAM said you will find the sweet spot for it and you can do the same every time.