The vent position is more a personal prefrence than a requirement of any position. Using an AMPs, I normally preheat to 275 with the vent closed. Then just before adding the AMPs to the smoking chamber I open the vent 100% to insure a good draft thru the chamber. 30 mins. later I will come back and regulate the vent for two reasons, it does allow less work by the heating element, thereby smoking with less heat, less smoke required, less chance of too much smoke. Too much smoke causes an incomplete burn and forms cresote. Stale air does not do it, incomplete combustion does.
Also as almost quickly skipped over above, regulating air flow also allows both a longer smoke from the AMPs as well as requiring less to be needed. I have gotten 18 to 20 hours smoke from my AMPs by regulation. With 100% vent I believe its 12 hours?
Vent open, vent regulated, vent shut, all when done properly will produce quality smoke. You just have to learn how to do each correctly.
There is no right or wrong, only what you decide is right for you. Easiest is vent full open, less chance of mistakes or needing to figure out how to regulate. Completely closed off is also easy, if you have the patience to learn. Regulated is the best of both worlds.