water pan in smokehouse

I would say in general that is true. But it all depends on the process. "Smoke cooking" say a rack of ribs, brisket, meatloaf and so on can benifit the meat and help keep it from drying out and maybe even add a little flavor if the water in the pan was flavored. (This could also be called BBQing) "Cold smoking" where you are just adding some smoke flavor to the meat or cheese being smoked for a short time or at a low temp usually under 110 degrees would generally not use a water pan. "Smoke curing" for longer periods and at varying temps would also not generally use water pans. Water pans in the little store bought units are multipurposed. They help regulate or stabilize the heat of the unit by providing a "mass" to hold and release heat. The water as it evaporates at or near steam temps from the pan provides a moist cooking media to the food. Should the heat near the meats surface become to high, the evaporation may add some cooling to help stablize the meats temp. The water pan provides a sheilding action to any heat source from meat drippings, and prevents fire flare ups from dripping grease.

Now the "Original" smokehouse was built mainly to protect the meat from pest like insects and animals and the weather while the meat cured/dried. So, yes traditionally moisture is what was trying to be removed. The smoke to keep the bugs away and then giving the meat a good flavor was a bonus!