I add moisture to either my kettle or my UDS, unless I am running them with a full load of meat. Usually, in my kettle, I will either have two soup cans full of water, or a cast iron skillet full of water in there. I believe that the added moisture makes for a better cooking atmosphere, offers less drying of the meat surface and moderates heat spike in the initial cook time. By the time I reach the stall, the moisture does not have an affect on how the evaporation of rendering process is going to proceed. But, I believe the added moisture does aid in not getting those jerky like surface characteristics.
I do not believe this is as important in a wood burning pit, or a gas put for that matter, as both of those processes actually release moisture as a part of the combustion of their respective fuel. But, since I burn charcoal, a fuel sources that has already had the moisture driven off, this makes a difference.
I came to this thinking, in part, because I noticed that my best cooks have occurred either at night, or on rainy/drizzly days, where the air is naturally more humid.
The SS Platypus, sails again, to the support of the Vets!
"perhaps...but then again...maybe not..."