Hi just wondering why is it good keep airflow at minimum during first part of roast? What affect does airflow have for a dense bean and low density bean?

I keep the dampers closed until I get to the point where the beans start releasing moisture (usually 225-250 degrees). I want to get from dump to the start of dry as quickly as possible without scorching the beans

When you charge beans they start releasing moisture..
With low air flow they are in a steam bath like environment and transfer more heat to each other more easily..
When they turn yellow you increase air and just before 1C you increase air again..