Interesting question and answers.
If charcoal is your fuel then insulation is needed for stability of temp and low consumption of fuel.
To what point insulation becomes a bad thing is when the cooker holds so much heat 1 briquette keeps the temp then there is no chance of any wood added to do its then is a clean way.
Meaning, if you look at the chimney starters when the coal is fully lit, there is flames.
spread those coals out in a grill and no flames just glowing coals.
I personally believe flames are the cleanest smoke, smoke with aroma and flavor.
Using my offset early on, I stuck with coals and found I needed to insulate it.
Wind, outside air temps would affect the cook chamber.
After insulating it is very stable.
Problem now that I use wood, because running small fires really heat up the chamber.
Running small fires is a lot of work because they burn up fast and need constant attention.